The ultrasonic surface wave induced by the laser shock processing and its propagation in half-space elastic plate with micro crack were simulated with Abaqus software based on equivalent load method, and the effects of the size of the micro cracks on the ultrasonic signal were also discussed. The pulsed laser was equivalent to a load with Gaussian profile in time and space, and the relationship between the physical parameters of the laser and the load was established by the correction factor. On the basis of verifying the correctness of the finite element model and equivalent load method, the effect of the crack width and depth on the acoustic characteristics of reflection wave and transmission wave was discussed. The results show that the equivalent load method is effective to simulate the process of laser ultrasonic crack detection, and it is very important for the numerical simulation of laser ultrasonic and the application in the detection of the crack.