diff --git a/ddl/column.go b/ddl/column.go
index 60dc9dc1e057f..7578d81ec0ed5 100644
--- a/ddl/column.go
+++ b/ddl/column.go
@@ -688,7 +688,13 @@ func needChangeColumnData(oldCol, newCol *model.ColumnInfo) bool {
 	toUnsigned := mysql.HasUnsignedFlag(newCol.Flag)
 	originUnsigned := mysql.HasUnsignedFlag(oldCol.Flag)
 	needTruncationOrToggleSign := func() bool {
-		return newCol.Flen > 0 && newCol.Flen < oldCol.Flen || toUnsigned != originUnsigned
+		return (newCol.Flen > 0 && newCol.Flen < oldCol.Flen) || (toUnsigned != originUnsigned)
+	}
+	// Ignore the potential max display length represented by integer's flen, use default flen instead.
+	oldColFlen, _ := mysql.GetDefaultFieldLengthAndDecimal(oldCol.Tp)
+	newColFlen, _ := mysql.GetDefaultFieldLengthAndDecimal(newCol.Tp)
+	needTruncationOrToggleSignForInteger := func() bool {
+		return (newColFlen > 0 && newColFlen < oldColFlen) || (toUnsigned != originUnsigned)
 	}
 
 	// Deal with the same type.
@@ -700,6 +706,8 @@ func needChangeColumnData(oldCol, newCol *model.ColumnInfo) bool {
 			return oldCol.Flen != newCol.Flen || oldCol.Decimal != newCol.Decimal || toUnsigned != originUnsigned
 		case mysql.TypeEnum, mysql.TypeSet:
 			return isElemsChangedToModifyColumn(oldCol.Elems, newCol.Elems)
+		case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
+			return toUnsigned != originUnsigned
 		}
 
 		return needTruncationOrToggleSign()
@@ -715,7 +723,7 @@ func needChangeColumnData(oldCol, newCol *model.ColumnInfo) bool {
 	case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
 		switch newCol.Tp {
 		case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
-			return needTruncationOrToggleSign()
+			return needTruncationOrToggleSignForInteger()
 		}
 	case mysql.TypeFloat, mysql.TypeDouble:
 		switch newCol.Tp {
diff --git a/ddl/column_test.go b/ddl/column_test.go
index e080a7e3e6bd1..6dc9125208175 100644
--- a/ddl/column_test.go
+++ b/ddl/column_test.go
@@ -1152,7 +1152,7 @@ func (s *testColumnSuite) TestModifyColumn(c *C) {
 		err    error
 	}{
 		{"int", "bigint", nil},
-		{"int", "int unsigned", errUnsupportedModifyColumn.GenWithStackByArgs("length 10 is less than origin 11, and tidb_enable_change_column_type is false")},
+		{"int", "int unsigned", errUnsupportedModifyColumn.GenWithStackByArgs("can't change unsigned integer to signed or vice versa, and tidb_enable_change_column_type is false")},
 		{"varchar(10)", "text", nil},
 		{"varbinary(10)", "blob", nil},
 		{"text", "blob", errUnsupportedModifyCharset.GenWithStackByArgs("charset from utf8mb4 to binary")},
diff --git a/ddl/column_type_change_test.go b/ddl/column_type_change_test.go
index 4f3207d032b96..88a7333cda763 100644
--- a/ddl/column_type_change_test.go
+++ b/ddl/column_type_change_test.go
@@ -939,3 +939,51 @@ func (s *testColumnTypeChangeSuite) TestColumnTypeChangeFromNumericToOthers(c *C
 	tk.MustExec("alter table t modify b json")
 	tk.MustQuery("select * from t").Check(testkit.Rows("-258.12345 333.33 2000000.20000002 323232323.32323235 -111.11111450195312 -222222222222.22223 \"\\u0015\""))
 }
+
+// Test issue #20529.
+func (s *testColumnTypeChangeSuite) TestColumnTypeChangeIgnoreDisplayLength(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustExec("use test")
+	tk.Se.GetSessionVars().EnableChangeColumnType = true
+	defer func() {
+		tk.Se.GetSessionVars().EnableChangeColumnType = false
+	}()
+
+	originalHook := s.dom.DDL().GetHook()
+	defer s.dom.DDL().(ddl.DDLForTest).SetHook(originalHook)
+
+	var assertResult bool
+	assertHasAlterWriteReorg := func(tbl table.Table) {
+		// Restore the assert result to false.
+		assertResult = false
+		hook := &ddl.TestDDLCallback{}
+		hook.OnJobRunBeforeExported = func(job *model.Job) {
+			if tbl.Meta().ID != job.TableID {
+				return
+			}
+			if job.SchemaState == model.StateWriteReorganization {
+				assertResult = true
+			}
+		}
+		s.dom.DDL().(ddl.DDLForTest).SetHook(hook)
+	}
+
+	// Change int to tinyint.
+	// Although display length is increased, the default flen is decreased, reorg is needed.
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a int(1))")
+	tbl := testGetTableByName(c, tk.Se, "test", "t")
+	assertHasAlterWriteReorg(tbl)
+	tk.MustExec("alter table t modify column a tinyint(3)")
+	c.Assert(assertResult, Equals, true)
+
+	// Change tinyint to tinyint
+	// Although display length is decreased, default flen is the same, reorg is not needed.
+	tk.MustExec("drop table if exists t")
+	tk.MustExec("create table t(a tinyint(3))")
+	tbl = testGetTableByName(c, tk.Se, "test", "t")
+	assertHasAlterWriteReorg(tbl)
+	tk.MustExec("alter table t modify column a tinyint(1)")
+	c.Assert(assertResult, Equals, false)
+	tk.MustExec("drop table if exists t")
+}
diff --git a/ddl/ddl_api.go b/ddl/ddl_api.go
index f7acacd7d4ff6..9a577ca9ad158 100644
--- a/ddl/ddl_api.go
+++ b/ddl/ddl_api.go
@@ -3385,6 +3385,10 @@ func checkModifyCharsetAndCollation(toCharset, toCollate, origCharset, origColla
 // CheckModifyTypeCompatible checks whether changes column type to another is compatible considering
 // field length and precision.
 func CheckModifyTypeCompatible(origin *types.FieldType, to *types.FieldType) (allowedChangeColumnValueMsg string, err error) {
+	var (
+		toFlen     = to.Flen
+		originFlen = origin.Flen
+	)
 	unsupportedMsg := fmt.Sprintf("type %v not match origin %v", to.CompactStr(), origin.CompactStr())
 	var skipSignCheck bool
 	var skipLenCheck bool
@@ -3405,6 +3409,10 @@ func CheckModifyTypeCompatible(origin *types.FieldType, to *types.FieldType) (al
 	case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
 		switch to.Tp {
 		case mysql.TypeTiny, mysql.TypeShort, mysql.TypeInt24, mysql.TypeLong, mysql.TypeLonglong:
+			// For integers, we should ignore the potential display length represented by flen, using
+			// the default flen of the type.
+			originFlen, _ = mysql.GetDefaultFieldLengthAndDecimal(origin.Tp)
+			toFlen, _ = mysql.GetDefaultFieldLengthAndDecimal(to.Tp)
 			// Changing integer to integer, whether reorg is necessary is depend on the flen/decimal/signed.
 			skipSignCheck = true
 			skipLenCheck = true
@@ -3527,8 +3535,8 @@ func CheckModifyTypeCompatible(origin *types.FieldType, to *types.FieldType) (al
 		}
 	}
 
-	if to.Flen > 0 && to.Flen < origin.Flen {
-		msg := fmt.Sprintf("length %d is less than origin %d", to.Flen, origin.Flen)
+	if toFlen > 0 && toFlen < originFlen {
+		msg := fmt.Sprintf("length %d is less than origin %d", toFlen, originFlen)
 		if skipLenCheck {
 			return msg, errUnsupportedModifyColumn.GenWithStackByArgs(msg)
 		}
diff --git a/ddl/ddl_worker_test.go b/ddl/ddl_worker_test.go
index 6efa8df25e2df..301bbb43c65b1 100644
--- a/ddl/ddl_worker_test.go
+++ b/ddl/ddl_worker_test.go
@@ -456,7 +456,7 @@ func buildCancelJobTests(firstID int64) []testCancelJob {
 		{act: model.ActionShardRowID, jobIDs: []int64{firstID + 17}, cancelRetErrs: noErrs, cancelState: model.StateNone},
 
 		{act: model.ActionModifyColumn, jobIDs: []int64{firstID + 18}, cancelRetErrs: noErrs, cancelState: model.StateNone},
-		{act: model.ActionModifyColumn, jobIDs: []int64{firstID + 19}, cancelRetErrs: []error{admin.ErrCancelFinishedDDLJob.GenWithStackByArgs(firstID + 19)}, cancelState: model.StateDeleteOnly},
+		{act: model.ActionModifyColumn, jobIDs: []int64{firstID + 19}, cancelRetErrs: noErrs, cancelState: model.StateDeleteOnly},
 
 		{act: model.ActionAddForeignKey, jobIDs: []int64{firstID + 20}, cancelRetErrs: noErrs, cancelState: model.StateNone},
 		{act: model.ActionAddForeignKey, jobIDs: []int64{firstID + 21}, cancelRetErrs: []error{admin.ErrCancelFinishedDDLJob.GenWithStackByArgs(firstID + 21)}, cancelState: model.StatePublic},
@@ -773,7 +773,7 @@ func (s *testDDLSerialSuite) TestCancelJob(c *C) {
 	// modify none-state column
 	col.DefaultValue = "1"
 	updateTest(&tests[15])
-	modifyColumnArgs := []interface{}{col, col.Name, &ast.ColumnPosition{}, byte(0)}
+	modifyColumnArgs := []interface{}{col, col.Name, &ast.ColumnPosition{}, byte(0), uint64(0)}
 	doDDLJobErrWithSchemaState(ctx, d, c, dbInfo.ID, tblInfo.ID, test.act, modifyColumnArgs, &test.cancelState)
 	c.Check(checkErr, IsNil)
 	changedTable = testGetTable(c, d, dbInfo.ID, tblInfo.ID)
@@ -784,13 +784,14 @@ func (s *testDDLSerialSuite) TestCancelJob(c *C) {
 	col.FieldType.Tp = mysql.TypeTiny
 	col.FieldType.Flen = col.FieldType.Flen - 1
 	updateTest(&tests[16])
-	modifyColumnArgs = []interface{}{col, col.Name, &ast.ColumnPosition{}, byte(0)}
-	doDDLJobSuccess(ctx, d, c, dbInfo.ID, tblInfo.ID, test.act, modifyColumnArgs)
+	modifyColumnArgs = []interface{}{col, col.Name, &ast.ColumnPosition{}, byte(0), uint64(0)}
+	cancelState = model.StateNone
+	doDDLJobErrWithSchemaState(ctx, d, c, dbInfo.ID, tblInfo.ID, test.act, modifyColumnArgs, &cancelState)
 	c.Check(checkErr, IsNil)
 	changedTable = testGetTable(c, d, dbInfo.ID, tblInfo.ID)
 	changedCol = model.FindColumnInfo(changedTable.Meta().Columns, col.Name.L)
-	c.Assert(changedCol.FieldType.Tp, Equals, mysql.TypeTiny)
-	c.Assert(changedCol.FieldType.Flen, Equals, col.FieldType.Flen)
+	c.Assert(changedCol.FieldType.Tp, Equals, mysql.TypeLonglong)
+	c.Assert(changedCol.FieldType.Flen, Equals, col.FieldType.Flen+1)
 	col.FieldType.Flen++
 
 	// Test add foreign key failed cause by canceled.