Abstract: With the wide application of laser welding technology in automobile and rail transit, the requirements for non-destructive testing of laser welds are getting higher and higher. For the laser welding of two-layer metal sheets below 3 mm, the air-coupled ultrasonic testing technology is discussed. The possibility of detecting the laser weld. Using numerical analysis and experimental analysis, the Lamb wave is excited on the aluminum plate in the air, and laser welding is analyzed by the propagation simulation of the Lamb wave in the laser weld test piece. By studying the propagation simulation of Lamb waves in laser weld specimens, The effect of the width of the laser weld and the quality of the weld on the reflectivity and transmittance are analyzed. The results show that the Lamb wave A0 mode can be used to evaluate the quality of the laser weld.