diff --git a/cmd/explaintest/r/new_character_set_builtin.result b/cmd/explaintest/r/new_character_set_builtin.result
index a1e547c4219eb..c4fb7c8c7fca3 100644
--- a/cmd/explaintest/r/new_character_set_builtin.result
+++ b/cmd/explaintest/r/new_character_set_builtin.result
@@ -81,6 +81,12 @@ hex(convert('1' using gbk))	convert('1' using gbk)
 select hex(convert('ã…‚' using gbk)), convert('ã…‚' using gbk);
 hex(convert('ã…‚' using gbk))	convert('ã…‚' using gbk)
 3F	?
+select hex(convert(0xe240 using gbk)), convert(0xe240 using gbk);
+hex(convert(0xe240 using gbk))	convert(0xe240 using gbk)
+E240	釦
+select hex(convert(0x1e240 using gbk)), convert(0x1e240 using gbk);
+hex(convert(0x1e240 using gbk))	convert(0x1e240 using gbk)
+01E240	
釦
 select convert(a using binary), convert(convert(a using gbk) using binary) from t;
 convert(a using binary)	convert(convert(a using gbk) using binary)
 中文	ÖÐÎÄ
@@ -117,6 +123,12 @@ hex(convert('1' using gbk))	convert('1' using gbk)
 select hex(convert('ã…‚' using gbk)), convert('ã…‚' using gbk);
 hex(convert('ã…‚' using gbk))	convert('ã…‚' using gbk)
 3F	?
+select hex(convert(0xe240 using gbk)), convert(0xe240 using gbk);
+hex(convert(0xe240 using gbk))	convert(0xe240 using gbk)
+E240	釦
+select hex(convert(0x1e240 using gbk)), convert(0x1e240 using gbk);
+hex(convert(0x1e240 using gbk))	convert(0x1e240 using gbk)
+01E240	
釦
 select convert(a using binary) from t;
 convert(a using binary)
 中文
diff --git a/cmd/explaintest/t/new_character_set_builtin.test b/cmd/explaintest/t/new_character_set_builtin.test
index ff4c2a9354f74..fd92ed513f018 100644
--- a/cmd/explaintest/t/new_character_set_builtin.test
+++ b/cmd/explaintest/t/new_character_set_builtin.test
@@ -44,6 +44,8 @@ select hex(convert('å•Š' using gbk)), convert('å•Š' using gbk);
 select hex(convert('a' using gbk)), convert('a' using gbk);
 select hex(convert('1' using gbk)), convert('1' using gbk);
 select hex(convert('ã…‚' using gbk)), convert('ã…‚' using gbk);
+select hex(convert(0xe240 using gbk)), convert(0xe240 using gbk);
+select hex(convert(0x1e240 using gbk)), convert(0x1e240 using gbk);
 select convert(a using binary), convert(convert(a using gbk) using binary) from t;
 select convert(convert('中文' using gbk) using binary), convert('中文' using binary);
 select convert(convert('ã…‚' using gbk) using binary), convert('ã…‚' using binary);
@@ -54,6 +56,8 @@ select hex(convert('å•Š' using gbk)), convert('å•Š' using gbk);
 select hex(convert('a' using gbk)), convert('a' using gbk);
 select hex(convert('1' using gbk)), convert('1' using gbk);
 select hex(convert('ã…‚' using gbk)), convert('ã…‚' using gbk);
+select hex(convert(0xe240 using gbk)), convert(0xe240 using gbk);
+select hex(convert(0x1e240 using gbk)), convert(0x1e240 using gbk);
 select convert(a using binary) from t;
 select convert(convert('中文' using gbk) using binary), convert('中文' using binary);
 select convert(convert('ã…‚' using gbk) using binary), convert('ã…‚' using binary);
diff --git a/expression/builtin_string.go b/expression/builtin_string.go
index 38a5647d49fac..c15e4d4200920 100644
--- a/expression/builtin_string.go
+++ b/expression/builtin_string.go
@@ -1152,14 +1152,8 @@ func (b *builtinConvertSig) evalString(row chunk.Row) (string, bool, error) {
 	}
 	// if expr is binary string and convert meet error, we should return NULL.
 	if types.IsBinaryStr(b.args[0].GetType()) {
-		target, _, err := transform.String(encoding.NewEncoder(), expr)
-		if err != nil {
-			return "", true, err
-		}
-
-		// we should convert target into utf8 internal.
-		exprInternal, _, _ := transform.String(encoding.NewDecoder(), target)
-		return exprInternal, false, nil
+		exprInternal, _, err := transform.String(encoding.NewDecoder(), expr)
+		return exprInternal, err != nil, nil
 	}
 	if types.IsBinaryStr(b.tp) {
 		enc := charset.NewEncoding(b.args[0].GetType().Charset)
diff --git a/expression/builtin_string_vec.go b/expression/builtin_string_vec.go
index 34293d6103be0..5f51caefa7fec 100644
--- a/expression/builtin_string_vec.go
+++ b/expression/builtin_string_vec.go
@@ -685,7 +685,6 @@ func (b *builtinConvertSig) vecEvalString(input *chunk.Chunk, result *chunk.Colu
 	if encoding == nil {
 		return errUnknownCharacterSet.GenWithStackByArgs(b.tp.Charset)
 	}
-	encoder := encoding.NewEncoder()
 	decoder := encoding.NewDecoder()
 	isBinaryStr := types.IsBinaryStr(b.args[0].GetType())
 	isRetBinary := types.IsBinaryStr(b.tp)
@@ -702,13 +701,12 @@ func (b *builtinConvertSig) vecEvalString(input *chunk.Chunk, result *chunk.Colu
 		}
 		exprI := expr.GetString(i)
 		if isBinaryStr {
-			target, _, err := transform.String(encoder, exprI)
+			target, _, err := transform.String(decoder, exprI)
 			if err != nil {
-				return err
+				result.AppendNull()
+				continue
 			}
-			// we should convert target into utf8 internal.
-			exprInternal, _, _ := transform.String(decoder, target)
-			result.AppendString(exprInternal)
+			result.AppendString(target)
 		} else {
 			if isRetBinary {
 				str, err := enc.EncodeString(exprI)