Abstract: Laser ultrasonic technology was used to detect surface defects of the additive manufactured parts, and the finite element method was used to simulate the propagation process of laser-excited ultrasonic waves under the thermoelastic mechanism. The surface wave reflection signals received from different detection positions were analyzed, and the influence of the depth and width of defects on the surface wave reflection signal was studied. Laser ultrasonic testing experiments on 316 L stainless steel additive manufacturing parts verified the correctness of the model, and then the wavelet soft threshold denoising algorithm was used to process the collected laser ultrasound signal. The results showed that the numerical simulation was basically consistent with the experimental results. The arrival time difference of the RS wave and the RR wave generated by the surface wave and the defect could detect the depth of defects, and the width of defects had almost no effect on the detection result.