Abstract: This paper describes the laser ultrasonic technology based on opto-acoustic effect, which can solve the problem of low excitation efficiency of the traditional laser ultrasonic technique. In order to detect the internal defects in materials, the finite element analysis method is employed to simulate the interaction of laser ultrasonic and defects while the ultrasonic wave being propagating in the material, and the experiment is designed to verify the theoretical analysis. An OA probe is designed to improve the excitation efficiency and used to detect the internal defects of Al material. The results show that the method could detect the internal defects effectively.