diff --git a/benchmarks/benchmark_serving.py b/benchmarks/benchmark_serving.py
index 14e697a2ea5..a4bea94e6bd 100644
--- a/benchmarks/benchmark_serving.py
+++ b/benchmarks/benchmark_serving.py
@@ -474,8 +474,8 @@ async def limited_request_func(request_func_input, pbar):
             benchmark_outputs = outputs[half : n - half]
 
         # 根据收到最后一个chunk的时间戳计算总时长
-        if len(outputs) >= 2:
-            benchmark_duration = outputs[-1].end_timestamp - outputs[0].end_timestamp
+        if len(benchmark_outputs) >= 2:
+            benchmark_duration = benchmark_outputs[-1].end_timestamp - benchmark_outputs[0].end_timestamp
         else:
             benchmark_duration = 0.0