diff --git a/cmd/explaintest/r/explain_generate_column_substitute.result b/cmd/explaintest/r/explain_generate_column_substitute.result
index f61e8796fe168..5162adb37f49c 100644
--- a/cmd/explaintest/r/explain_generate_column_substitute.result
+++ b/cmd/explaintest/r/explain_generate_column_substitute.result
@@ -558,3 +558,15 @@ select * from PK_S_MULTI_30_tmp use index (eidx) where truncate(col1, 3) <= trun
 COL1	COL2	COL3
 -1.7976931348623157e308	0	0
 -1.7976931348623157e308	1	0
+create table t004(a date);
+insert into t004 values ('2021-08-20');
+select * from t004 where timestampadd(microsecond, 1, a) = timestampadd(microsecond, 1, '2021-08-20');
+a
+2021-08-20
+alter table t004 add index eidx ((timestampadd(microsecond, 1, a)));
+select * from t004 use index(eidx) where timestampadd(microsecond, 1, a) = timestampadd(microsecond, 1, '2021-08-20');
+a
+2021-08-20
+select * from t004 ignore index (eidx) where timestampadd(microsecond, 1, a) = timestampadd(microsecond, 1, '2021-08-20');
+a
+2021-08-20
diff --git a/cmd/explaintest/t/explain_generate_column_substitute.test b/cmd/explaintest/t/explain_generate_column_substitute.test
index 06a546a05c6e5..152d2c2a6dc7f 100644
--- a/cmd/explaintest/t/explain_generate_column_substitute.test
+++ b/cmd/explaintest/t/explain_generate_column_substitute.test
@@ -252,3 +252,10 @@ select * from  `PK_S_MULTI_30_tmp` ignore index (expression_index) where floor(c
 alter table PK_S_MULTI_30_tmp add index eidx ((truncate(col1, 3)));
 select * from PK_S_MULTI_30_tmp ignore index (eidx) where truncate(col1, 3) <= truncate(-1.7976931348623157e308, 3);
 select * from PK_S_MULTI_30_tmp use index (eidx) where truncate(col1, 3) <= truncate(-1.7976931348623157e308, 3);
+
+create table t004(a date);
+insert into t004 values ('2021-08-20');
+select * from t004 where timestampadd(microsecond, 1, a) = timestampadd(microsecond, 1, '2021-08-20');
+alter table t004 add index eidx ((timestampadd(microsecond, 1, a)));
+select * from t004 use index(eidx) where timestampadd(microsecond, 1, a) = timestampadd(microsecond, 1, '2021-08-20');
+select * from t004 ignore index (eidx) where timestampadd(microsecond, 1, a) = timestampadd(microsecond, 1, '2021-08-20');
diff --git a/expression/builtin_time.go b/expression/builtin_time.go
index dcaac7b8556e7..e6a61019a40e6 100644
--- a/expression/builtin_time.go
+++ b/expression/builtin_time.go
@@ -6714,7 +6714,20 @@ func (c *timestampAddFunctionClass) getFunction(ctx sessionctx.Context, args []E
 	if err != nil {
 		return nil, err
 	}
-	bf.tp = &types.FieldType{Tp: mysql.TypeString, Flen: mysql.MaxDatetimeWidthNoFsp, Decimal: types.UnspecifiedLength}
+	flen := mysql.MaxDatetimeWidthNoFsp
+	con, ok := args[0].(*Constant)
+	if !ok {
+		return nil, errors.New("should not happened")
+	}
+	unit, null, err := con.EvalString(ctx, chunk.Row{})
+	if null || err != nil {
+		return nil, errors.New("should not happened")
+	}
+	if unit == ast.TimeUnitMicrosecond.String() {
+		flen = mysql.MaxDatetimeWidthWithFsp
+	}
+
+	bf.tp.Flen = flen
 	sig := &builtinTimestampAddSig{bf}
 	sig.setPbCode(tipb.ScalarFuncSig_TimestampAdd)
 	return sig, nil
diff --git a/expression/typeinfer_test.go b/expression/typeinfer_test.go
index 8cba8c5ef6b8f..9c526712419ec 100644
--- a/expression/typeinfer_test.go
+++ b/expression/typeinfer_test.go
@@ -1232,13 +1232,14 @@ func (s *InferTypeSuite) createTestCase4TimeFuncs() []typeInferTestCase {
 		{`date_format('2017-06-15', '%r%r%r%r')`, mysql.TypeVarString, charset.CharsetUTF8MB4, mysql.NotNullFlag, 44, types.UnspecifiedLength},
 		{`date_format(151113102019.12, '%r%r%r%r')`, mysql.TypeVarString, charset.CharsetUTF8MB4, mysql.NotNullFlag, 44, types.UnspecifiedLength},
 
-		{"timestampadd(HOUR, c_int_d, c_timestamp_d)", mysql.TypeString, charset.CharsetUTF8MB4, 0, 19, types.UnspecifiedLength},
-		{"timestampadd(minute, c_double_d, c_timestamp_d)", mysql.TypeString, charset.CharsetUTF8MB4, 0, 19, types.UnspecifiedLength},
-		{"timestampadd(SeconD, c_int_d, c_char)", mysql.TypeString, charset.CharsetUTF8MB4, 0, 19, types.UnspecifiedLength},
-		{"timestampadd(SeconD, c_varchar, c_time_d)", mysql.TypeString, charset.CharsetUTF8MB4, 0, 19, types.UnspecifiedLength},
-		{"timestampadd(SeconD, c_int_d, c_datetime)", mysql.TypeString, charset.CharsetUTF8MB4, 0, 19, types.UnspecifiedLength},
-		{"timestampadd(SeconD, c_double_d, c_bchar)", mysql.TypeString, charset.CharsetUTF8MB4, 0, 19, types.UnspecifiedLength},
-		{"timestampadd(SeconD, c_int_d, c_blob_d)", mysql.TypeString, charset.CharsetUTF8MB4, 0, 19, types.UnspecifiedLength},
+		{"timestampadd(HOUR, c_int_d, c_timestamp_d)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthNoFsp, types.UnspecifiedLength},
+		{"timestampadd(minute, c_double_d, c_timestamp_d)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthNoFsp, types.UnspecifiedLength},
+		{"timestampadd(SeconD, c_int_d, c_char)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthNoFsp, types.UnspecifiedLength},
+		{"timestampadd(SeconD, c_varchar, c_time_d)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthNoFsp, types.UnspecifiedLength},
+		{"timestampadd(SeconD, c_int_d, c_datetime)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthNoFsp, types.UnspecifiedLength},
+		{"timestampadd(SeconD, c_double_d, c_bchar)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthNoFsp, types.UnspecifiedLength},
+		{"timestampadd(SeconD, c_int_d, c_blob_d)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthNoFsp, types.UnspecifiedLength},
+		{"timestampadd(microsecond, c_int_d, c_blob_d)", mysql.TypeVarString, charset.CharsetUTF8MB4, 0, mysql.MaxDatetimeWidthWithFsp, types.UnspecifiedLength},
 
 		{"to_seconds(c_char)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, 20, 0},
 		{"to_days(c_char)", mysql.TypeLonglong, charset.CharsetBin, mysql.BinaryFlag, 20, 0},