diff --git a/paddle/fluid/imperative/tracer.cc b/paddle/fluid/imperative/tracer.cc
index ec8b4f9eead141e8dd9d75a33dc32b808c90bc5c..ce107daa1586829af091136af35f9da151fc1514 100644
--- a/paddle/fluid/imperative/tracer.cc
+++ b/paddle/fluid/imperative/tracer.cc
@@ -230,10 +230,12 @@ void Tracer::TraceBackward(const std::shared_ptr<OpBase>& fwd_op,
               VLOG(3) << op->Type();
             }
           }
+          auto grad_name = (*(fwd_var_iter->second))->GradVarBase()->Name();
           if (!grad_pending_ops.empty()) {
             for (const auto& op : grad_pending_ops) {
-              PADDLE_ENFORCE_NOT_NULL(op,
-                                      "No nullptr should be grad_pending op");
+              PADDLE_ENFORCE_NOT_NULL(
+                  op, "No nullptr should be grad_pending op for variable %s ",
+                  grad_name);
               if (visited_preceding_ops.count(op) == 0) {
                 visited_preceding_ops.insert(op);
                 grad_op->InsertGradPendingOps(op);