To improve the efficiency of ultrasonic testing for plastic bonded explosive(PBX) materials, and ensure the reliability and safety of the final product, a non-contact and nondestructive testing method of internal defects in PBX based on laser ultrasonic technique was studied. Based on thermo-elastic mechanism, a finite element numerical calculation method and model for the laser ultrasound of PBX material were established. The distribution of internal transient temperature and ultrasound fields of PBX material under the pulsed laser irradiation was obtained.The interaction between the laser ultrasound with the internal hole and crack defects of PBX was simulated. The numerical results show that using 5 laser beam to stimulate simultaneously, it can greatly improve the detection ability of laser ultrasound on internal defect within the safety temperature range of PBX. The detection of the cracks with length of more than 0.5 mm and the holes with diameter of more than 0.2 mm can be realized. The feasibility of laser ultrasound for the internal defect detection of PBX materials is preliminarily validated