diff --git a/ddl/db_partition_test.go b/ddl/db_partition_test.go
index 78629e4dbc073..b597b0ce95700 100644
--- a/ddl/db_partition_test.go
+++ b/ddl/db_partition_test.go
@@ -26,6 +26,7 @@ import (
 	"github.com/pingcap/parser/model"
 	tmysql "github.com/pingcap/parser/mysql"
 	"github.com/pingcap/tidb/ddl"
+	"github.com/pingcap/tidb/ddl/testutil"
 	"github.com/pingcap/tidb/domain"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/meta"
@@ -952,7 +953,7 @@ func (s *testIntegrationSuite) TestPartitionDropIndex(c *C) {
 	}
 	c.Assert(idx1, NotNil)
 
-	sessionExecInGoroutine(c, s.store, "drop index idx1 on partition_drop_idx;", done)
+	testutil.SessionExecInGoroutine(c, s.store, "drop index idx1 on partition_drop_idx;", done)
 	ticker := time.NewTicker(s.lease / 2)
 	defer ticker.Stop()
 LOOP:
diff --git a/ddl/db_test.go b/ddl/db_test.go
index 72f2237d8193c..8ddb68b2a9e27 100644
--- a/ddl/db_test.go
+++ b/ddl/db_test.go
@@ -32,6 +32,7 @@ import (
 	tmysql "github.com/pingcap/parser/mysql"
 	"github.com/pingcap/parser/terror"
 	"github.com/pingcap/tidb/ddl"
+	testddlutil "github.com/pingcap/tidb/ddl/testutil"
 	"github.com/pingcap/tidb/domain"
 	"github.com/pingcap/tidb/infoschema"
 	"github.com/pingcap/tidb/kv"
@@ -608,7 +609,7 @@ func (s *testDBSuite) testAddIndex(c *C, testPartition bool, createTableSQL stri
 	s.mustExec(c, sql)
 	otherKeys = append(otherKeys, v)
 
-	sessionExecInGoroutine(c, s.store, "create index c3_index on test_add_index (c3)", done)
+	testddlutil.SessionExecInGoroutine(c, s.store, "create index c3_index on test_add_index (c3)", done)
 
 	deletedKeys := make(map[int]struct{})
 
@@ -726,7 +727,6 @@ LOOP:
 		delete(handles, h)
 	}
 	c.Assert(handles, HasLen, 0)
-
 	s.tk.MustExec("drop table test_add_index")
 }
 
@@ -754,7 +754,7 @@ func (s *testDBSuite) TestDropIndex(c *C) {
 	}
 	c.Assert(c3idx, NotNil)
 
-	sessionExecInGoroutine(c, s.store, "drop index c3_index on test_drop_index", done)
+	testddlutil.SessionExecInGoroutine(c, s.store, "drop index c3_index on test_drop_index", done)
 
 	ticker := time.NewTicker(s.lease / 2)
 	defer ticker.Stop()
@@ -916,38 +916,6 @@ func sessionExec(c *C, s kv.Storage, sql string) {
 	se.Close()
 }
 
-func sessionExecInGoroutine(c *C, s kv.Storage, sql string, done chan error) {
-	execMultiSQLInGoroutine(c, s, "test_db", []string{sql}, done)
-}
-
-func execMultiSQLInGoroutine(c *C, s kv.Storage, dbName string, multiSQL []string, done chan error) {
-	go func() {
-		se, err := session.CreateSession4Test(s)
-		if err != nil {
-			done <- errors.Trace(err)
-			return
-		}
-		defer se.Close()
-		_, err = se.Execute(context.Background(), "use "+dbName)
-		if err != nil {
-			done <- errors.Trace(err)
-			return
-		}
-		for _, sql := range multiSQL {
-			rs, err := se.Execute(context.Background(), sql)
-			if err != nil {
-				done <- errors.Trace(err)
-				return
-			}
-			if rs != nil {
-				done <- errors.Errorf("RecordSet should be empty.")
-				return
-			}
-			done <- nil
-		}
-	}()
-}
-
 func (s *testDBSuite) testAddColumn(c *C) {
 	done := make(chan error, 1)
 
@@ -957,7 +925,7 @@ func (s *testDBSuite) testAddColumn(c *C) {
 		s.mustExec(c, "insert into t2 values (?, ?, ?)", i, i, i)
 	}
 
-	sessionExecInGoroutine(c, s.store, "alter table t2 add column c4 int default -1", done)
+	testddlutil.SessionExecInGoroutine(c, s.store, "alter table t2 add column c4 int default -1", done)
 
 	ticker := time.NewTicker(s.lease / 2)
 	defer ticker.Stop()
@@ -1092,7 +1060,7 @@ func (s *testDBSuite) testDropColumn(c *C) {
 	}
 
 	// get c4 column id
-	sessionExecInGoroutine(c, s.store, "alter table t2 drop column c4", done)
+	testddlutil.SessionExecInGoroutine(c, s.store, "alter table t2 drop column c4", done)
 
 	ticker := time.NewTicker(s.lease / 2)
 	defer ticker.Stop()
@@ -1151,9 +1119,9 @@ func (s *testDBSuite) TestDropColumn(c *C) {
 	for i := 0; i < num/2; i++ {
 		multiDDL = append(multiDDL, "alter table t2 add column c4 int", "alter table t2 drop column c4")
 	}
-	execMultiSQLInGoroutine(c, s.store, "drop_col_db", multiDDL, ddlDone)
+	testddlutil.ExecMultiSQLInGoroutine(c, s.store, "drop_col_db", multiDDL, ddlDone)
 	for i := 0; i < num; i++ {
-		execMultiSQLInGoroutine(c, s.store, "drop_col_db", []string{"insert into t2 set c1 = 1, c2 = 1, c3 = 1, c4 = 1"}, dmlDone)
+		testddlutil.ExecMultiSQLInGoroutine(c, s.store, "drop_col_db", []string{"insert into t2 set c1 = 1, c2 = 1, c3 = 1, c4 = 1"}, dmlDone)
 	}
 	for i := 0; i < num; i++ {
 		select {
@@ -1524,7 +1492,7 @@ func (s *testDBSuite) TestAddNotNullColumn(c *C) {
 	s.tk.MustExec("create table tnn (c1 int primary key auto_increment, c2 int)")
 	s.tk.MustExec("insert tnn (c2) values (0)" + strings.Repeat(",(0)", 99))
 	done := make(chan error, 1)
-	sessionExecInGoroutine(c, s.store, "alter table tnn add column c3 int not null default 3", done)
+	testddlutil.SessionExecInGoroutine(c, s.store, "alter table tnn add column c3 int not null default 3", done)
 	updateCnt := 0
 out:
 	for {
diff --git a/ddl/failtest/fail_db_test.go b/ddl/failtest/fail_db_test.go
index bcb2d21d914e6..491704bca3eb9 100644
--- a/ddl/failtest/fail_db_test.go
+++ b/ddl/failtest/fail_db_test.go
@@ -18,17 +18,21 @@ import (
 	"fmt"
 	"math/rand"
 	"os"
+	"sync/atomic"
 	"testing"
 	"time"
 
 	. "github.com/pingcap/check"
+	"github.com/pingcap/errors"
 	gofail "github.com/pingcap/gofail/runtime"
 	"github.com/pingcap/parser"
 	"github.com/pingcap/parser/model"
 	"github.com/pingcap/tidb/ddl"
+	"github.com/pingcap/tidb/ddl/testutil"
 	"github.com/pingcap/tidb/domain"
 	"github.com/pingcap/tidb/kv"
 	"github.com/pingcap/tidb/session"
+	"github.com/pingcap/tidb/sessionctx/variable"
 	"github.com/pingcap/tidb/store/mockstore"
 	"github.com/pingcap/tidb/store/mockstore/mocktikv"
 	"github.com/pingcap/tidb/util/logutil"
@@ -311,3 +315,61 @@ func (s *testFailDBSuite) TestGenGlobalIDFail(c *C) {
 	tk.MustExec("admin check table t1")
 	tk.MustExec("admin check table t2")
 }
+
+func (s *testFailDBSuite) TestAddIndexWorkerNum(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("create database if not exists test_db")
+	tk.MustExec("use test_db")
+	tk.MustExec("drop table if exists test_add_index")
+	tk.MustExec("create table test_add_index (c1 bigint, c2 bigint, c3 bigint, primary key(c1))")
+
+	done := make(chan error, 1)
+	start := -10
+	num := 4096
+	// first add some rows
+	for i := start; i < num; i++ {
+		sql := fmt.Sprintf("insert into test_add_index values (%d, %d, %d)", i, i, i)
+		tk.MustExec(sql)
+	}
+
+	is := s.dom.InfoSchema()
+	schemaName := model.NewCIStr("test_db")
+	tableName := model.NewCIStr("test_add_index")
+	tbl, err := is.TableByName(schemaName, tableName)
+	c.Assert(err, IsNil)
+
+	splitCount := 100
+	// Split table to multi region.
+	s.cluster.SplitTable(s.mvccStore, tbl.Meta().ID, splitCount)
+
+	originDDLAddIndexWorkerCnt := variable.GetDDLReorgWorkerCounter()
+	lastSetWorkerCnt := originDDLAddIndexWorkerCnt
+	atomic.StoreInt32(&ddl.TestCheckWorkerNumber, lastSetWorkerCnt)
+	ddl.TestCheckWorkerNumber = lastSetWorkerCnt
+	defer variable.SetDDLReorgWorkerCounter(originDDLAddIndexWorkerCnt)
+
+	gofail.Enable("github.com/pingcap/tidb/ddl/checkIndexWorkerNum", `return(true)`)
+	defer gofail.Disable("github.com/pingcap/tidb/ddl/checkIndexWorkerNum")
+
+	testutil.SessionExecInGoroutine(c, s.store, "create index c3_index on test_add_index (c3)", done)
+	checkNum := 0
+
+LOOP:
+	for {
+		select {
+		case err = <-done:
+			if err == nil {
+				break LOOP
+			}
+			c.Assert(err, IsNil, Commentf("err:%v", errors.ErrorStack(err)))
+		case <-ddl.TestCheckWorkerNumCh:
+			lastSetWorkerCnt = int32(rand.Intn(8) + 8)
+			tk.MustExec(fmt.Sprintf("set @@tidb_ddl_reorg_worker_cnt=%d", lastSetWorkerCnt))
+			atomic.StoreInt32(&ddl.TestCheckWorkerNumber, lastSetWorkerCnt)
+			checkNum++
+		}
+	}
+	c.Assert(checkNum, Greater, 5)
+	tk.MustExec("admin check table test_add_index")
+	tk.MustExec("drop table test_add_index")
+}
diff --git a/ddl/index.go b/ddl/index.go
index a35d39feca527..2dafb9b66ef2a 100644
--- a/ddl/index.go
+++ b/ddl/index.go
@@ -823,7 +823,7 @@ func (w *addIndexWorker) handleBackfillTask(d *ddlCtx, task *reorgIndexTask) *ad
 	if task.endIncluded {
 		rightParenthesis = "]"
 	}
-	log.Infof("[ddl-reorg] worker(%v), finish region %v ranges [%v,%v%s, addedCount:%v, scanCount:%v, nextHandle:%v, elapsed time(s):%v",
+	log.Infof("[ddl-reorg] worker(%v), finish table %v ranges [%v,%v%s, addedCount:%v, scanCount:%v, nextHandle:%v, elapsed time(s):%v",
 		w.id, task.physicalTableID, task.startHandle, task.endHandle, rightParenthesis, result.addedCount, result.scanCount, result.nextHandle, time.Since(startTime).Seconds())
 
 	return result
@@ -1046,34 +1046,12 @@ func (w *worker) sendRangeTaskToWorkers(t table.Table, workers []*addIndexWorker
 	return nil, nil
 }
 
-// buildIndexForReorgInfo build backfilling tasks from [reorgInfo.StartHandle, reorgInfo.EndHandle),
-// and send these tasks to add index workers, till we finish adding the indices.
-func (w *worker) buildIndexForReorgInfo(t table.PhysicalTable, workers []*addIndexWorker, job *model.Job, reorgInfo *reorgInfo) error {
-	totalAddedCount := job.GetRowCount()
-
-	startHandle, endHandle := reorgInfo.StartHandle, reorgInfo.EndHandle
-	for {
-		kvRanges, err := splitTableRanges(t, reorgInfo.d.store, startHandle, endHandle)
-		if err != nil {
-			return errors.Trace(err)
-		}
-
-		log.Infof("[ddl-reorg] start to reorg index of %v region ranges, handle range:[%v, %v).", len(kvRanges), startHandle, endHandle)
-		remains, err := w.sendRangeTaskToWorkers(t, workers, reorgInfo, &totalAddedCount, kvRanges)
-		if err != nil {
-			return errors.Trace(err)
-		}
-
-		if len(remains) == 0 {
-			break
-		}
-		startHandle, _, err = decodeHandleRange(remains[0])
-		if err != nil {
-			return errors.Trace(err)
-		}
-	}
-	return nil
-}
+var (
+	// TestCheckWorkerNumCh use for test adjust add index worker.
+	TestCheckWorkerNumCh = make(chan struct{}, 0)
+	// TestCheckWorkerNumber use for test adjust add index worker.
+	TestCheckWorkerNumber = int32(16)
+)
 
 // addPhysicalTableIndex handles the add index reorganization state for a non-partitioned table or a partition.
 // For a partitioned table, it should be handled partition by partition.
@@ -1092,6 +1070,9 @@ func (w *worker) buildIndexForReorgInfo(t table.PhysicalTable, workers []*addInd
 func (w *worker) addPhysicalTableIndex(t table.PhysicalTable, indexInfo *model.IndexInfo, reorgInfo *reorgInfo) error {
 	job := reorgInfo.Job
 	log.Infof("[ddl-reorg] addTableIndex, job:%s, reorgInfo:%#v", job, reorgInfo)
+	totalAddedCount := job.GetRowCount()
+
+	startHandle, endHandle := reorgInfo.StartHandle, reorgInfo.EndHandle
 	sessCtx := newContext(reorgInfo.d.store)
 	decodeColMap, err := makeupDecodeColMap(sessCtx, t, indexInfo)
 	if err != nil {
@@ -1100,16 +1081,68 @@ func (w *worker) addPhysicalTableIndex(t table.PhysicalTable, indexInfo *model.I
 
 	// variable.ddlReorgWorkerCounter can be modified by system variable "tidb_ddl_reorg_worker_cnt".
 	workerCnt := variable.GetDDLReorgWorkerCounter()
-	idxWorkers := make([]*addIndexWorker, workerCnt)
-	for i := 0; i < int(workerCnt); i++ {
-		sessCtx := newContext(reorgInfo.d.store)
-		idxWorkers[i] = newAddIndexWorker(sessCtx, w, i, t, indexInfo, decodeColMap)
-		idxWorkers[i].priority = job.Priority
-		go idxWorkers[i].run(reorgInfo.d)
-	}
-	defer closeAddIndexWorkers(idxWorkers)
-	err = w.buildIndexForReorgInfo(t, idxWorkers, job, reorgInfo)
-	return errors.Trace(err)
+	idxWorkers := make([]*addIndexWorker, 0, workerCnt)
+	defer func() {
+		closeAddIndexWorkers(idxWorkers)
+	}()
+
+	for {
+		kvRanges, err := splitTableRanges(t, reorgInfo.d.store, startHandle, endHandle)
+		if err != nil {
+			return errors.Trace(err)
+		}
+
+		// For dynamic adjust add index worker number.
+		workerCnt = variable.GetDDLReorgWorkerCounter()
+		// If only have 1 range, we can only start 1 worker.
+		if len(kvRanges) < int(workerCnt) {
+			workerCnt = int32(len(kvRanges))
+		}
+		// Enlarge the worker size.
+		for i := len(idxWorkers); i < int(workerCnt); i++ {
+			sessCtx := newContext(reorgInfo.d.store)
+			idxWorker := newAddIndexWorker(sessCtx, w, i, t, indexInfo, decodeColMap)
+			idxWorker.priority = job.Priority
+			idxWorkers = append(idxWorkers, idxWorker)
+			go idxWorkers[i].run(reorgInfo.d)
+		}
+		// Shrink the worker size.
+		if len(idxWorkers) > int(workerCnt) {
+			workers := idxWorkers[workerCnt:]
+			idxWorkers = idxWorkers[:workerCnt]
+			closeAddIndexWorkers(workers)
+		}
+
+		// gofail: var checkIndexWorkerNum bool
+		// if checkIndexWorkerNum {
+		//	num := int(atomic.LoadInt32(&TestCheckWorkerNumber))
+		//	if num != 0 {
+		//		if num > len(kvRanges) {
+		//			if len(idxWorkers) != len(kvRanges) {
+		//				return errors.Errorf("check index worker num error, len kv ranges is: %v, check index worker num is: %v, actual index num is: %v", len(kvRanges), num, len(idxWorkers))
+		//			}
+		//		} else if num != len(idxWorkers) {
+		//			return errors.Errorf("check index worker num error, len kv ranges is: %v, check index worker num is: %v, actual index num is: %v", len(kvRanges), num, len(idxWorkers))
+		//		}
+		//		TestCheckWorkerNumCh <- struct{}{}
+		//	}
+		//}
+
+		log.Infof("[ddl-reorg] start %d workers to reorg index of %v region ranges, handle range:[%v, %v).", len(idxWorkers), len(kvRanges), startHandle, endHandle)
+		remains, err := w.sendRangeTaskToWorkers(t, idxWorkers, reorgInfo, &totalAddedCount, kvRanges)
+		if err != nil {
+			return errors.Trace(err)
+		}
+
+		if len(remains) == 0 {
+			break
+		}
+		startHandle, _, err = decodeHandleRange(remains[0])
+		if err != nil {
+			return errors.Trace(err)
+		}
+	}
+	return nil
 }
 
 // addTableIndex handles the add index reorganization state for a table.
diff --git a/ddl/testutil/testutil.go b/ddl/testutil/testutil.go
new file mode 100644
index 0000000000000..c690b05af3108
--- /dev/null
+++ b/ddl/testutil/testutil.go
@@ -0,0 +1,57 @@
+// Copyright 2018 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package testutil
+
+import (
+	"context"
+
+	"github.com/pingcap/check"
+	"github.com/pingcap/errors"
+	"github.com/pingcap/tidb/kv"
+	"github.com/pingcap/tidb/session"
+)
+
+// SessionExecInGoroutine export for testing.
+func SessionExecInGoroutine(c *check.C, s kv.Storage, sql string, done chan error) {
+	ExecMultiSQLInGoroutine(c, s, "test_db", []string{sql}, done)
+}
+
+// ExecMultiSQLInGoroutine exports for testing.
+func ExecMultiSQLInGoroutine(c *check.C, s kv.Storage, dbName string, multiSQL []string, done chan error) {
+	go func() {
+		se, err := session.CreateSession4Test(s)
+		if err != nil {
+			done <- errors.Trace(err)
+			return
+		}
+		defer se.Close()
+		_, err = se.Execute(context.Background(), "use "+dbName)
+		if err != nil {
+			done <- errors.Trace(err)
+			return
+		}
+		for _, sql := range multiSQL {
+			rs, err := se.Execute(context.Background(), sql)
+			if err != nil {
+				done <- errors.Trace(err)
+				return
+			}
+			if rs != nil {
+				done <- errors.Errorf("RecordSet should be empty.")
+				return
+			}
+			done <- nil
+		}
+	}()
+}