Experiments of ultrasonic testing stress of PBX-9003 explosive were carried out under a big load. The sonic elastic modulus of PBX-9003 explosive was obtained. The results show that the ultrasonic velocity propagating through explosive has a distinctive change when it receives a big load. The stress tested by ultrasonic method is close to the stress loaded by mechanical method. The feasibility of ultrasonic nondestructive testing the large stress of PBX-9003 explosive is verified.