diff --git a/src/sql/engine/expr/ob_expr_substr.cpp b/src/sql/engine/expr/ob_expr_substr.cpp
index f82704280..3c29f0189 100644
--- a/src/sql/engine/expr/ob_expr_substr.cpp
+++ b/src/sql/engine/expr/ob_expr_substr.cpp
@@ -234,7 +234,11 @@ int ObExprSubstr::calc_result_typeN(ObExprResType &type,
     if (OB_SUCC(ret)
         && ob_is_text_tc(type.get_type())
         && 3 == param_num
-        && !types_array[2].get_param().is_null()) {
+        && !types_array[2].get_param().is_null()
+        // Compatible with mixing running different versions of observer, the result type is
+        // varchar only when all observer versions are higher than 4.2.0, otherwise is blob,
+        // which is not compatible with mysql
+        && GET_MIN_CLUSTER_VERSION() >= CLUSTER_VERSION_4_2_0_0) {
       const ObObj &len_obj = types_array[2].get_param();
       int64_t substr_len = len_obj.is_int() ? len_obj.get_int() : 0;
       if (substr_len > 0 && substr_len <= OB_MAX_CAST_CHAR_VARCHAR_LENGTH) {