diff --git a/expression/builtin_string.go b/expression/builtin_string.go
index c494d9fcb5c10..acac019139708 100644
--- a/expression/builtin_string.go
+++ b/expression/builtin_string.go
@@ -1150,7 +1150,7 @@ func (b *builtinConvertSig) evalString(row chunk.Row) (string, bool, error) {
 		return string(ret), false, err
 	}
 	enc := charset.FindEncoding(resultTp.Charset)
-	if !charset.IsValidString(enc, expr) {
+	if !enc.IsValid(hack.Slice(expr)) {
 		replace, _ := enc.Transform(nil, hack.Slice(expr), charset.OpReplace)
 		return string(replace), false, nil
 	}
diff --git a/expression/builtin_string_vec.go b/expression/builtin_string_vec.go
index 3da555f9319ed..202a3d74ed3f1 100644
--- a/expression/builtin_string_vec.go
+++ b/expression/builtin_string_vec.go
@@ -689,7 +689,7 @@ func (b *builtinConvertSig) vecEvalString(input *chunk.Chunk, result *chunk.Colu
 			continue
 		}
 		exprI := expr.GetBytes(i)
-		if !charset.IsValid(enc, exprI) {
+		if !enc.IsValid(exprI) {
 			encBuf, _ = enc.Transform(encBuf, exprI, charset.OpReplace)
 			result.AppendBytes(encBuf)
 		} else {
diff --git a/expression/collation.go b/expression/collation.go
index 8dc5df02e55e0..813560775e2b4 100644
--- a/expression/collation.go
+++ b/expression/collation.go
@@ -22,6 +22,7 @@ import (
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/util/chunk"
 	"github.com/pingcap/tidb/util/collate"
+	"github.com/pingcap/tidb/util/hack"
 	"github.com/pingcap/tidb/util/logutil"
 )
 
@@ -315,7 +316,7 @@ func safeConvert(ctx sessionctx.Context, ec *ExprCollation, args ...Expression)
 			if isNull {
 				continue
 			}
-			if !charset.IsValidString(enc, str) {
+			if !enc.IsValid(hack.Slice(str)) {
 				return false
 			}
 		} else {
diff --git a/parser/charset/encoding.go b/parser/charset/encoding.go
index 92b1433549860..bf3d6b8ff269c 100644
--- a/parser/charset/encoding.go
+++ b/parser/charset/encoding.go
@@ -57,7 +57,7 @@ type Encoding interface {
 	Tp() EncodingTp
 	// Peek returns the next char.
 	Peek(src []byte) []byte
-	// IsValid checks whether a utf-8 string is valid in the current encoding.
+	// IsValid checks whether the utf-8 bytes can be convert to valid string in current encoding.
 	IsValid(src []byte) bool
 	// Foreach iterates the characters in in current encoding.
 	Foreach(src []byte, op Op, fn func(from, to []byte, ok bool) bool)
@@ -103,21 +103,6 @@ const (
 	OpDecodeReplace = opToUTF8 | opTruncateReplace | opCollectTo
 )
 
-// IsValid checks whether the bytes is valid in current encoding.
-func IsValid(e Encoding, src []byte) bool {
-	isValid := true
-	e.Foreach(src, opFromUTF8, func(from, to []byte, ok bool) bool {
-		isValid = ok
-		return ok
-	})
-	return isValid
-}
-
-// IsValidString is a string version of IsValid.
-func IsValidString(e Encoding, str string) bool {
-	return IsValid(e, Slice(str))
-}
-
 // CountValidBytes counts the first valid bytes in src that
 // can be encode to the current encoding.
 func CountValidBytes(e Encoding, src []byte) int {
diff --git a/parser/charset/encoding_test.go b/parser/charset/encoding_test.go
index a78aa640d8be5..27d41dbf5ebd2 100644
--- a/parser/charset/encoding_test.go
+++ b/parser/charset/encoding_test.go
@@ -133,8 +133,7 @@ func TestEncodingValidate(t *testing.T) {
 			enc = charset.EncodingUTF8MB3StrictImpl
 		}
 		strBytes := []byte(tc.str)
-		ok := charset.IsValid(enc, strBytes)
-		require.Equal(t, tc.ok, ok, msg)
+		require.Equal(t, tc.ok, enc.IsValid(strBytes), msg)
 		replace, _ := enc.Transform(nil, strBytes, charset.OpReplace)
 		require.Equal(t, tc.expected, string(replace), msg)
 	}
diff --git a/parser/charset/encoding_utf8.go b/parser/charset/encoding_utf8.go
index 6c7d79941a31d..499ce5ea50de7 100644
--- a/parser/charset/encoding_utf8.go
+++ b/parser/charset/encoding_utf8.go
@@ -77,7 +77,7 @@ func (e *encodingUTF8) IsValid(src []byte) bool {
 
 // Transform implements Encoding interface.
 func (e *encodingUTF8) Transform(dest, src []byte, op Op) ([]byte, error) {
-	if IsValid(e, src) {
+	if e.IsValid(src) {
 		return src, nil
 	}
 	return e.encodingBase.Transform(dest, src, op)
@@ -120,7 +120,7 @@ func (e *encodingUTF8MB3Strict) Foreach(src []byte, op Op, fn func(srcCh, dstCh
 
 // Transform implements Encoding interface.
 func (e *encodingUTF8MB3Strict) Transform(dest, src []byte, op Op) ([]byte, error) {
-	if IsValid(e, src) {
+	if e.IsValid(src) {
 		return src, nil
 	}
 	return e.encodingBase.Transform(dest, src, op)