diff --git a/deps/oblib/src/lib/charset/ob_charset.cpp b/deps/oblib/src/lib/charset/ob_charset.cpp
index 27b1b8742a..662b869784 100644
--- a/deps/oblib/src/lib/charset/ob_charset.cpp
+++ b/deps/oblib/src/lib/charset/ob_charset.cpp
@@ -3141,10 +3141,10 @@ int ObCharsetUtils::init(ObIAllocator &allocator)
   return ret;
 }
 
-bool ObStringScanner::next_character(ObString &encoding, int32_t &wchar, int &ret)
+bool ObStringScanner::next_character(ObString &encoding_value, int32_t &unicode_value, int &ret)
 {
   bool has_next = false;
-  ret = next_character(encoding, wchar);
+  ret = next_character(encoding_value, unicode_value);
 
   if (OB_ITER_END == ret) {
     has_next = false;
@@ -3158,20 +3158,26 @@ bool ObStringScanner::next_character(ObString &encoding, int32_t &wchar, int &re
   return has_next;
 }
 
-int ObStringScanner::next_character(ObString &encoding, int32_t &wchar)
+int ObStringScanner::next_character(ObString &encoding_value, int32_t &unicode_value)
 {
   int ret = OB_SUCCESS;
   int32_t length = 0;
 
-  ObString &str = const_cast<ObString &>(str_);
+  ObString &str = str_;
 
   if (str.empty()) {
     ret = OB_ITER_END;
-  } else if (OB_FAIL(ObCharset::mb_wc(collation_type_, str.ptr(), str.length(), length, wchar))) {
-    ret = OB_ERR_INCORRECT_STRING_VALUE;
-    LOG_WARN("fail to call mb_wc", K(ret), KPHEX(str.ptr(), str.length()));
-  } else {
-    encoding.assign_ptr(str.ptr(), length);
+  } else if (OB_FAIL(ObCharset::mb_wc(collation_type_, str.ptr(), str.length(), length, unicode_value))) {
+    if (!!(IGNORE_INVALID_CHARACTER & flags_)) {
+      ret = OB_SUCCESS;
+      length = 1;
+    } else {
+      ret = OB_ERR_INCORRECT_STRING_VALUE;
+      LOG_WARN("fail to call mb_wc", K(ret), KPHEX(str.ptr(), str.length()));
+    }
+  }
+  if (OB_SUCC(ret)) {
+    encoding_value.assign_ptr(str.ptr(), length);
     LOG_DEBUG("next_character", K(ret), KPHEX(str.ptr(), str.length()));
     str += length;
   }
diff --git a/deps/oblib/src/lib/charset/ob_charset.h b/deps/oblib/src/lib/charset/ob_charset.h
index 12443cec5b..80d22a974b 100644
--- a/deps/oblib/src/lib/charset/ob_charset.h
+++ b/deps/oblib/src/lib/charset/ob_charset.h
@@ -608,15 +608,22 @@ private:
 class ObStringScanner
 {
 public:
-  ObStringScanner(const ObString &str, common::ObCollationType collation_type)
-    : str_(str), collation_type_(collation_type)
+  enum {
+    IGNORE_INVALID_CHARACTER = 1<<0,
+  };
+  ObStringScanner(const ObString &str, common::ObCollationType collation_type, uint64_t flags = 0)
+    : origin_str_(str), str_(str), collation_type_(collation_type), flags_(flags)
   {}
-  int next_character(ObString &encoding, int32_t &wchar);
-  bool next_character(ObString &encoding, int32_t &wchar, int &ret);
+  int next_character(ObString &encoding_value, int32_t &unicode_value);
+  bool next_character(ObString &encoding_value, int32_t &unicode_value, int &ret);
+  ObString get_remain_str() { return str_; }
+  void forward_bytes(int64_t n) { str_ += n; }
   TO_STRING_KV(K_(str), K_(collation_type));
 private:
-  const ObString &str_;
+  const ObString &origin_str_;
+  ObString str_;
   common::ObCollationType collation_type_;
+  uint64_t flags_;
 };
 
 class ObCharSetString
diff --git a/src/sql/engine/expr/ob_expr_replace.cpp b/src/sql/engine/expr/ob_expr_replace.cpp
index 5db20b1e75..0b1d9db0db 100644
--- a/src/sql/engine/expr/ob_expr_replace.cpp
+++ b/src/sql/engine/expr/ob_expr_replace.cpp
@@ -131,9 +131,10 @@ int ObExprReplace::replace(ObString &ret_str,
                            ObExprStringBuf &string_buf)
 {
   int ret = OB_SUCCESS;
+  ObString dst_str;
+  bool is_null = false;
   if (OB_UNLIKELY(text.length() <= 0)) {
     // Return empty string
-    ret_str.reset();
   } else if (OB_UNLIKELY(from.length() <= 0) || OB_UNLIKELY(to.length() < 0)) {
     ret_str = text;
   } else if (OB_ISNULL(from.ptr())) {
@@ -142,51 +143,29 @@ int ObExprReplace::replace(ObString &ret_str,
   } else if (OB_UNLIKELY(text.length() < from.length()) ||
              OB_UNLIKELY(from == to)) {
     ret_str = text;
+  } else if (OB_FAIL(ObSQLUtils::check_well_formed_str(text, cs_type, dst_str, is_null, false, false))
+            || OB_FAIL(ObSQLUtils::check_well_formed_str(from, cs_type, dst_str, is_null, false, false))
+            || OB_FAIL(ObSQLUtils::check_well_formed_str(to, cs_type, dst_str, is_null, false, false))) {
+    LOG_WARN("check well formed str failed", K(ret));
   } else {
     ObSEArray<uint32_t, 4> locations(common::ObModIds::OB_SQL_EXPR_REPLACE,
                                      common::OB_MALLOC_NORMAL_BLOCK_SIZE);
-    const char *buf_start = text.ptr();
-    const char *buf_end = text.ptr() + text.length();
-    const ObCharsetInfo *cs = NULL;
-    int error = 0;
-    if (OB_UNLIKELY(OB_ISNULL(cs = ObCharset::get_charset(cs_type)) ||
-            OB_ISNULL(cs->cset))) {
-      ret = OB_ERR_UNEXPECTED;
-      LOG_ERROR("unexpected error. invalid argument(s)", K(cs_type));
-    }
-    int32_t char_len = 0;
-    int32_t next_char_len = 0;
-    while (OB_SUCC(ret) && OB_LIKELY(error == 0) && buf_start + char_len < buf_end) {
-      char_len += static_cast<int32_t>(cs->cset->well_formed_len(cs, buf_start + char_len, buf_end, 1, &error));
-      if (OB_UNLIKELY(0 != error)) {
-        bool is_null = false;
-        //mysql strict mode will return null, otherwise will return something
-        //so we should get session to acquire if is_strict mode here.
-        //we now set is_strict=false.
-        if (OB_FAIL(ObSQLUtils::check_well_formed_str(text, cs_type, ret_str, is_null, false, false))) {
-          LOG_WARN("check well formed str failed", K(ret));
-        }
-      } else if (next_char_len == 0 && FALSE_IT(next_char_len = char_len)) {
-      } else if (char_len < from.length()) {
-        //do nothing
-      } else if (char_len > from.length()) {
-        buf_start += next_char_len;
-        char_len = 0;
-        next_char_len = 0;
-      } else if (0 == MEMCMP(buf_start, from.ptr(), char_len)) {
-        ret = locations.push_back(buf_start - text.ptr());
-        buf_start += char_len;
-        char_len = 0;
-        next_char_len = 0;
+    ObString mb;
+    int32_t wc;
+    ObStringScanner scanner(text, cs_type, ObStringScanner::IGNORE_INVALID_CHARACTER);
+    while (OB_SUCC(ret) && scanner.get_remain_str().length() >= from.length()) {
+      if (0 == MEMCMP(scanner.get_remain_str().ptr(), from.ptr(), from.length())) {
+        ret = locations.push_back(scanner.get_remain_str().ptr() - text.ptr());
+        scanner.forward_bytes(from.length());
+      } else if (OB_FAIL(scanner.next_character(mb, wc))) {
+        LOG_WARN("get next character failed", K(ret));
       } else {
-        buf_start += next_char_len;
-        char_len = 0;
-        next_char_len = 0;
+        //do nothing
       }
     }
+
     int64_t tot_length = 0;
-    if (OB_UNLIKELY(error != 0)) {
-    } else if (OB_FAIL(ret)) {
+    if (OB_FAIL(ret)) {
       ret_str.reset();
     } else if (locations.count() == 0) {
       ret_str = text;
@@ -253,7 +232,7 @@ int ObExprReplace::eval_replace(const ObExpr &expr, ObEvalCtx &ctx, ObDatum &exp
     expr_datum.set_datum(*text);
   } else if (!is_lob_res) { // non text tc inputs
     if (OB_FAIL(replace(res,
-                        expr.args_[0]->datum_meta_.cs_type_,
+                        expr.datum_meta_.cs_type_,
                         text->get_string(),
                         !from->is_null() ? from->get_string() : ObString(),
                         (NULL != to && !to->is_null()) ? to->get_string() : ObString(),
@@ -288,7 +267,7 @@ int ObExprReplace::eval_replace(const ObExpr &expr, ObEvalCtx &ctx, ObDatum &exp
       LOG_WARN("failed to get string data", K(ret), K(expr.args_[2]->datum_meta_));
     }
     if (OB_SUCC(ret)) {
-      if (OB_FAIL(replace(res, expr.args_[0]->datum_meta_.cs_type_, text_data, from_data, to_data, temp_allocator))) {
+      if (OB_FAIL(replace(res, expr.datum_meta_.cs_type_, text_data, from_data, to_data, temp_allocator))) {
         LOG_WARN("do replace for lob resutl failed", K(ret), K(expr.datum_meta_.type_));
       } else if (OB_FAIL(ObTextStringHelper::string_to_templob_result(expr, ctx, expr_datum, res))) {
         LOG_WARN("set lob result failed", K(ret));
diff --git a/src/sql/resolver/ddl/ob_create_table_stmt.cpp b/src/sql/resolver/ddl/ob_create_table_stmt.cpp
index bfcf3d7f9e..a8313dfeab 100644
--- a/src/sql/resolver/ddl/ob_create_table_stmt.cpp
+++ b/src/sql/resolver/ddl/ob_create_table_stmt.cpp
@@ -93,7 +93,8 @@ int ObCreateTableStmt::get_first_stmt(ObString &first_stmt)
                                                   first_stmt,
                                                   get_query_ctx()->get_sql_stmt_coll_type(),
                                                   ObCharset::get_system_collation(),
-                                                  first_stmt))) {
+                                                  first_stmt,
+                                                  ObCharset::REPLACE_UNKNOWN_CHARACTER))) {
       LOG_WARN("fail to convert charset", K(ret), K(first_stmt),
                "stmt collation type", get_query_ctx()->get_sql_stmt_coll_type());
     }
diff --git a/src/sql/resolver/ddl/ob_ddl_stmt.cpp b/src/sql/resolver/ddl/ob_ddl_stmt.cpp
index 0a7b7faa5d..1358e8d7bc 100644
--- a/src/sql/resolver/ddl/ob_ddl_stmt.cpp
+++ b/src/sql/resolver/ddl/ob_ddl_stmt.cpp
@@ -34,7 +34,8 @@ int ObDDLStmt::get_first_stmt(ObString &first_stmt)
                                                 first_stmt,
                                                 get_query_ctx()->get_sql_stmt_coll_type(),
                                                 ObCharset::get_system_collation(),
-                                                first_stmt))) {
+                                                first_stmt,
+                                                ObCharset::REPLACE_UNKNOWN_CHARACTER))) {
     LOG_WARN("fail to convert charset", K(ret), K(first_stmt),
              "stmt collation type", get_query_ctx()->get_sql_stmt_coll_type());
   }