This is an experiment of the damage examination of plate material with the application of elastic waves. By use of two ultrasonic probe attached to the surface of plate material, elastic waves can be injected into the structure and the probe can also receive the echo signal. By comparing the received echo signal of the defect structure and of an intact structure, the purpose of recognizing the existence of defects was achieved by extracting the signal reflection caused by the defective components. A comprehensive research based on ultrasonic wave for nondestructive testing experimental system was done. The Ultrasonic flaw detector produces high–frequency and high–voltage pulse signals and it stimulates the actuators to transmit the elastic waves into the plate material. Another probe receives the echo signals, and as to the diagnosis of the extraction of the echo signal, a good method will be adopted: By the method of continuous wavelet transform, and then study the distribution of time domain and frequency domain. By comparing echo signal, the purpose of identifying the existence of defects is achieved by extracting the echo signal caused by the defective components.