diff --git a/expression/bench_test.go b/expression/bench_test.go
index 1d926fd6cb1e6..8f721297d0214 100644
--- a/expression/bench_test.go
+++ b/expression/bench_test.go
@@ -711,7 +711,7 @@ func (g *randHexStrGener) gen() interface{} {
 	return string(buf)
 }
 
-// dateTimeGener is used to generate a dataTime
+// dateTimeGener is used to generate a dateTime
 type dateTimeGener struct {
 	Fsp     int
 	Year    int
@@ -740,7 +740,7 @@ func (g *dateTimeGener) gen() interface{} {
 	return t
 }
 
-// dateTimeStrGener is used to generate strings which are dataTime format
+// dateTimeStrGener is used to generate strings which are dateTime format
 type dateTimeStrGener struct {
 	Fsp     int
 	Year    int
@@ -762,14 +762,14 @@ func (g *dateTimeStrGener) gen() interface{} {
 	hour := g.randGen.Intn(12)
 	minute := g.randGen.Intn(60)
 	second := g.randGen.Intn(60)
-	dataTimeStr := fmt.Sprintf("%d-%d-%d %d:%d:%d",
+	dateTimeStr := fmt.Sprintf("%d-%d-%d %d:%d:%d",
 		g.Year, g.Month, g.Day, hour, minute, second)
 	if g.Fsp > 0 && g.Fsp <= 6 {
 		microFmt := fmt.Sprintf(".%%0%dd", g.Fsp)
-		return dataTimeStr + fmt.Sprintf(microFmt, g.randGen.Int()%(10^g.Fsp))
+		return dateTimeStr + fmt.Sprintf(microFmt, g.randGen.Int()%(10^g.Fsp))
 	}
 
-	return dataTimeStr
+	return dateTimeStr
 }
 
 // dateStrGener is used to generate strings which are date format
diff --git a/expression/builtin_time.go b/expression/builtin_time.go
index ee36fc7d6a8e6..6faad8387add4 100644
--- a/expression/builtin_time.go
+++ b/expression/builtin_time.go
@@ -5559,6 +5559,9 @@ func (b *builtinAddStringAndStringSig) evalString(row chunk.Row) (result string,
 	if isNull || err != nil {
 		return "", isNull, err
 	}
+	if !isDuration(arg1Str) {
+		return "", true, nil
+	}
 	sc := b.ctx.GetSessionVars().StmtCtx
 	arg1, err = types.ParseDuration(sc, arg1Str, getFsp4TimeAddSub(arg1Str))
 	if err != nil {
diff --git a/expression/builtin_time_vec_generated.go b/expression/builtin_time_vec_generated.go
index 535c54b9138b6..633d7ef8558d8 100644
--- a/expression/builtin_time_vec_generated.go
+++ b/expression/builtin_time_vec_generated.go
@@ -404,6 +404,10 @@ func (b *builtinAddStringAndStringSig) vecEvalString(input *chunk.Chunk, result
 
 		// calculate
 
+		if !isDuration(arg1) {
+			result.AppendNull() // fixed: false
+			continue
+		}
 		sc := b.ctx.GetSessionVars().StmtCtx
 		arg1Duration, err := types.ParseDuration(sc, arg1, getFsp4TimeAddSub(arg1))
 		if err != nil {
diff --git a/expression/generator/time_vec.go b/expression/generator/time_vec.go
index bb6b4c5fd2be4..a415d94685364 100644
--- a/expression/generator/time_vec.go
+++ b/expression/generator/time_vec.go
@@ -54,7 +54,7 @@ import (
 {{ end }}
 {{ define "SetNull" }}{{if .Output.Fixed}}result.SetNull(i, true){{else}}result.AppendNull(){{end}} // fixed: {{.Output.Fixed }}{{ end }}
 {{ define "ConvertStringToDuration" }}
-		{{ if and (ne .SigName "builtinAddStringAndStringSig") (ne .SigName "builtinSubStringAndStringSig") }}
+		{{ if (ne .SigName "builtinSubStringAndStringSig") }}
 		if !isDuration(arg1) {
 			{{ template "SetNull" . }}
 			continue
@@ -852,7 +852,7 @@ var timeDiffSigsTmpl = []sig{
 	{SigName: "builtinTimeTimeTimeDiffSig", TypeA: TypeDatetime, TypeB: TypeDatetime, Output: TypeDuration},
 }
 
-var addDataSigsTmpl = []sig{
+var addDateSigsTmpl = []sig{
 	{SigName: "builtinAddDateStringStringSig", TypeA: TypeString, TypeB: TypeString, Output: TypeDatetime},
 	{SigName: "builtinAddDateStringIntSig", TypeA: TypeString, TypeB: TypeInt, Output: TypeDatetime},
 	{SigName: "builtinAddDateStringRealSig", TypeA: TypeString, TypeB: TypeReal, Output: TypeDatetime},
@@ -871,7 +871,7 @@ var addDataSigsTmpl = []sig{
 	{SigName: "builtinAddDateDurationDecimalSig", TypeA: TypeDuration, TypeB: TypeDecimal, Output: TypeDuration},
 }
 
-var subDataSigsTmpl = []sig{
+var subDateSigsTmpl = []sig{
 	{SigName: "builtinSubDateStringStringSig", TypeA: TypeString, TypeB: TypeString, Output: TypeDatetime},
 	{SigName: "builtinSubDateStringIntSig", TypeA: TypeString, TypeB: TypeInt, Output: TypeDatetime},
 	{SigName: "builtinSubDateStringRealSig", TypeA: TypeString, TypeB: TypeReal, Output: TypeDatetime},
@@ -912,8 +912,8 @@ var tmplVal = struct {
 		{FuncName: "AddTime", Sigs: addTimeSigsTmpl},
 		{FuncName: "SubTime", Sigs: subTimeSigsTmpl},
 		{FuncName: "TimeDiff", Sigs: timeDiffSigsTmpl},
-		{FuncName: "AddDate", Sigs: addDataSigsTmpl},
-		{FuncName: "SubDate", Sigs: subDataSigsTmpl},
+		{FuncName: "AddDate", Sigs: addDateSigsTmpl},
+		{FuncName: "SubDate", Sigs: subDateSigsTmpl},
 	},
 }
 
@@ -931,11 +931,11 @@ func generateDotGo(fileName string) error {
 	if err != nil {
 		return err
 	}
-	err = addOrSubDate.Execute(w, function{FuncName: "AddDate", Sigs: addDataSigsTmpl})
+	err = addOrSubDate.Execute(w, function{FuncName: "AddDate", Sigs: addDateSigsTmpl})
 	if err != nil {
 		return err
 	}
-	err = addOrSubDate.Execute(w, function{FuncName: "SubDate", Sigs: subDataSigsTmpl})
+	err = addOrSubDate.Execute(w, function{FuncName: "SubDate", Sigs: subDateSigsTmpl})
 	if err != nil {
 		return err
 	}
diff --git a/expression/integration_test.go b/expression/integration_test.go
index 6ebf5e35d1b52..9b1f143d95bd0 100644
--- a/expression/integration_test.go
+++ b/expression/integration_test.go
@@ -1668,6 +1668,8 @@ func (s *testIntegrationSuite2) TestTimeBuiltin(c *C) {
 	tk.MustQuery(`select addtime(cast(1 as time), cast(1 as time))`).Check(testkit.Rows("00:00:02"))
 	tk.MustQuery(`select addtime(cast(null as time), cast(1 as time))`).Check(testkit.Rows("<nil>"))
 	tk.MustQuery(`select addtime(cast(1 as time), cast(null as time))`).Check(testkit.Rows("<nil>"))
+	tk.MustQuery(`select addtime("2020-05-13 14:01:24", "2020-04-29 05:11:19")`).Check(testkit.Rows("<nil>"))
+	tk.MustQuery(`select addtime("2020-05-13 14:01:24", "-2020-04-29 05:11:19")`).Check(testkit.Rows("<nil>"))
 
 	// for SUBTIME
 	result = tk.MustQuery("select subtime('01:01:11', '00:00:01.013'), subtime('01:01:11.00', '00:00:01'), subtime" +