Abstract: Regular examination of irradiated nuclear fuel assembly is of great significance to the safe operation of reactors and the performance study of nuclear fuel assemblies at high burnup. In order to observe the defects and the changes of the internal structure of irradiated fuel assembly without disassembling or destroying the fuel assembly, high energy X-ray computed tomography (X-ray CT) technology can be applied to the examination of irradiated fuel assembly. Japan has been devoting itself to the research of high-energy X-ray non-destructive detection technology for nuclear fuel assembly for many years. It is the only country in the world to develop a high resolution X-ray CT device for the detection of irradiated fuel assembly and to apply it to the field examination of reactor. In this paper, the structure, working principle, research status and some application examples of the fuel assembly X-ray CT device developed by JAEA in Japan are introduced in detail on the basis of combing the relevant research results in Japan in recent decades. which can provide reference for the development of nuclear fuel assembly detection technology device in China.