Abstract: Pointing at the poor ability to find the radial defect perpendicular to the outer surface in the engine disk and ring, this paper describes the principle and features of the bottom wave monitor method. According to test results, the monitoring method of bottom wave can effectively find defects perpendicular to the end plate and the nonuniformity in the material. So proposed method is called the back wave monitoring test method and it can avoid the undetected defects effectively.