Abstract: Fuel assembly damage directly influences the safe operation of the reactor. Analyzing the cause of fuel assembly damage is the key process of the fuel assembly development and improvement. This paper established the thermal chamber inspection method for the damaged fuel assembly, by studying the key technologies such as underwater collapsing, localizing the break and taking crevasse samples of the fuel assembly. The study shows the technical route is rational, and the method is practicable, which have provided technical approaches to check the damaged fuel assembly in a hot cell.