In order to solve the problem that the false anomaly generated by the reflection of reinforcement in the nondestructive testing of concrete defects interferes with the diagnosis and discrimination of defects，we carry out an experimental study on the reflection and defect of reinforcement in precast beam concrete. We discuss the influence of the steel bar distributed in different directions on the ultrasonic S-wave 3D imaging test results，establish the suspected defect group and the control group，and apply the ultrasonic method for comparison and verification，and obtain the false abnormal characteristics of the reflection of vertical and oblique steel bar. The results show that the false anomaly generated by the vertical distribution of steel bars is easy to identify，while the false anomaly generated by the oblique distribution of steel bar has a higher similarity with the true anomaly generated by the effective reflection wave from the defect，and produces a greater interference to the anomaly identification. Data interpretation should be combined with design drawings to strengthen identification，so as to avoid misjudgment.