In order to improve the generation efficiency of laser ultrasonic without damaging the measured surface, the spatial distribution of the laser source was changed, and the pulsed ring laser source was used. Using the finite element method, the numerical simulation of the full field ultrasonic wave generated in the aluminum plate was carried out by COMSOL Multiphysics. The generation characteristics of the superposition shear wave on the central axis of the ring laser source were studied, which vary with laser parameters. By simulating the change law of the ultrasonic field caused by defects, a method of detecting cracks on both sides of the ring laser source was proposed. The feasibility and effectiveness of defect detection by superposition shear wave were verified by simulating the change rule of ultrasonic field caused by defects. The results show that the generation efficiency can be significantly improved by using the ring laser source because ring light source loss is usually less than 50%. The direction of shear wave propagation is stable. The superposition depth of the shear wave is related to the ring radius, and the ring half-width can affect the intensity of the wave. The results provide a reference for the application of ring laser source generated ultrasonic in defect detection.