With the wide application of laser welding technology in automobiles and rail transportation,the non-destructive testing techno-logy for laser welding seams is also getting better.Aiming at the laser welding seam of two-layer metal sheet below 3 mm,the possibility of laser welding seam detection by air-coupling ultrasonic detection technology is discussed.By numerical analysis and experimental analysis,Lamb wave is excited on aluminum plate in air.Through the propagation simulation of Lamb wave in laser weld specimen,the influence of laser weld width and weld quality on reflectivity and transmittance is analyzed.The propagation law of Lamb wave in laser weld specimen is clarified.The results show that the quality of laser weld can be evaluated by the mode of Lamb wave A0.