Abstract: In the test, A0 mode Lame waves were excited by an air-coupled ultrasonic probe on the aluminum plate. Lame waves were excited and received on the same side of the aluminum plate containing damage, and defects were scanned with a step of 1mm. The wavelet coefficient envelope signal at 400 kHz frequency is extracted by continuous wavelet transform for the received signal, and the mode of excited Lame wave is identified. Furthermore, the amplitude envelope imaging is carried out using the continuous wavelet transform coefficient envelope signals received at different scanning points. The results show that the amplitude envelope signal noise at a specific frequency obtained by continuous wavelet transform is better and the imaging results have higher focusing.