diff --git a/python/paddle/tensor/stat.py b/python/paddle/tensor/stat.py
index 57a498b52dd7936d1bf3cc1bced4f1f04980aaea..7275dc3242fd3bc531c2c5381f9974a93c9a4205 100644
--- a/python/paddle/tensor/stat.py
+++ b/python/paddle/tensor/stat.py
@@ -151,7 +151,7 @@ def std(input, axis=None, keepdim=False, unbiased=True, out=None, name=None):
 
     tmp = var(input, axis=axis, keepdim=keepdim, unbiased=unbiased, name=name)
     tmp = layers.sqrt(tmp)
-    if out:
+    if out is not None:
         layers.assign(input=tmp, output=out)
         return out
     else: