Abstract: In the acousto-ultrasonic technique, it is essential for successful application of the technique to understand the propagation characteristics of ultrasonic wave. An FEM method was used to investigate the acousto-ultrasonic wave propagation. The simulating signal was processed by 2-DFFT to recognize the modes and compare with the theoretical parameter curve of the frequency versus wave number spectrum. It had been found that the dominant acousto-ultrasonic wave produced were multimode lamb waves. In order to show the acousto-ultrasonic wave propagation, the results were presented in from of snapshots. It was approved that combine the numerical analysis with experiment was an efficiency way in the ultrasonic testing.