diff --git a/paddle/fluid/operators/checkpoint_load_op.cc b/paddle/fluid/operators/checkpoint_load_op.cc
index d24c7819990f04e633358bacaa62e735f940e71e..a9676de369b4b45a097835ad104e37f745742ec5 100644
--- a/paddle/fluid/operators/checkpoint_load_op.cc
+++ b/paddle/fluid/operators/checkpoint_load_op.cc
@@ -114,7 +114,7 @@ class CheckpointLoadOp : public framework::OperatorBase {
     std::string dir = Attr<std::string>("dir");
     std::string serial_num_attr = Attr<std::string>("Serial");
 
-    PADDLE_ENFORCE(IsNumber(serial_num_attr),
+    PADDLE_ENFORCE(!IsNumber(serial_num_attr),
                    "Checkpoint Serial must be a number");
 
     std::string serial_var_name = std::string(SERIAL_VAR);
@@ -124,7 +124,8 @@ class CheckpointLoadOp : public framework::OperatorBase {
                    serial_var_name);
 
     auto *serial_num = serial_var->GetMutable<std::string>();
-    serial_num = serial_num_attr;
+    serial_num->clear();
+    serial_num->append(serial_num_attr);
 
     VLOG(1) << "CheckpointLoadOp set " << SERIAL_VAR
             << " value: " << serial_num;
diff --git a/paddle/fluid/operators/checkpoint_op_test.cc b/paddle/fluid/operators/checkpoint_op_test.cc
index 2acce227d23de5862784831e67fed3dc1b4c3a41..5312225e5f95230ff1e0946c7925c8b89253b3bd 100644
--- a/paddle/fluid/operators/checkpoint_op_test.cc
+++ b/paddle/fluid/operators/checkpoint_op_test.cc
@@ -69,6 +69,8 @@ TEST(CheckpointLoadOp, CPU) {
   }
 
   scope.Var("SERIAL_NUMBER");
+  auto* serial_num = scope.FindVar("SERIAL_NUMBER")->GetMutable<std::string>();
+  serial_num->append("0");
 
   paddle::framework::AttributeMap attrs;
   attrs.insert({"dir", std::string("ckpt")});
diff --git a/paddle/fluid/operators/checkpoint_save_op.cc b/paddle/fluid/operators/checkpoint_save_op.cc
index bab979e4074a613219bca8971b5b32250616eac6..30eda30c5f52fb3eea6c58015400a65161de3cf9 100644
--- a/paddle/fluid/operators/checkpoint_save_op.cc
+++ b/paddle/fluid/operators/checkpoint_save_op.cc
@@ -94,8 +94,8 @@ class CheckpointSaveOp : public framework::OperatorBase {
     VLOG(1) << "CheckpointSaveOp get " << SERIAL_VAR
             << " value: " << serial_num;
 
-    if (!IsNumber(serial_num)) {
-      serial_num = "0";
+    if (serial_num->empty()) {
+      serial_num->append("0");
     }
 
     std::string dir = GenePath(ck_dir, serial_num->c_str());