Abstract: The control rod driving mechanism (CRDM) is an important component of nuclear power plant, and the structure and connection form of the European Pressurized Reactor (EPR) CRDM are quite different from those of the CPR1000 Reactor. The change of CRDM pressure housing inspection method from visual and acoustic emission inspection to ultrasonic test was therefore required. According to the characteristics of its dissimilar metal welds and thin wall thickness, as well as the special space arrangement and radiation environment, the automatic ultrasonic inspection technology of CRDM dissimilar metal welds was studied. In this paper, ultrasonic testing technology and automatic inspection device are introduced. The test results show that the developed automatic ultrasonic inspection technique can effectively detect the defects in the simulated test blocks and the automatic ultrasonic inspection device can meet the requirements of field inspection.