The paper presents an experiment on the thermal shock damage of JOB-9003 and its evolution course in water under different temperatures (from 2 ℃ to 24 ℃,26 ℃,28 ℃,30 ℃,32 ℃) by using digital ultrasonic testing system. The intensity of the different damage accumulation degree (damage factor) has been tested. A fitted curve relationship between ultrasonic characteristic parameters (especially ultrasonic gain) and the damage accumulation degree of JOB-9003 explosives was found. It′s measured that the threshold (D_C) of the damage of JOB-9003 explosives is 0.223. The results prove that ultrasonic testing method is reliable to study the thermal shock damage of JOB-9003 and its evolution course,and provide the technique supports on studying dynamic state response of explosive to different load conditions.