diff --git a/python/paddle/fluid/tests/unittests/test_reader_reset.py b/python/paddle/fluid/tests/unittests/test_reader_reset.py
index 8ad11d76f683d556f05cafc3251acc942efef72f..a115c37e1df3fab98f105fa55f2f049dbcd98929 100644
--- a/python/paddle/fluid/tests/unittests/test_reader_reset.py
+++ b/python/paddle/fluid/tests/unittests/test_reader_reset.py
@@ -41,6 +41,8 @@ class TestReaderReset(unittest.TestCase):
                 self.data_file_name, reader, feeder)
 
     def setUp(self):
+        # set parallel threads to fit 20 batches in line 49
+        os.environ['CPU_NUM'] = str(20)
         self.use_cuda = fluid.core.is_compiled_with_cuda()
         self.data_file_name = './reader_reset_test.recordio'
         self.ins_shape = [3]