Abstract: By analyzing the reactor fuel assembly structure, a fuel assembly dismantling process is obtained, which includes overturning, removing the tube socket and finally extracting the fuel rods. This process can be adapted for narrow space and is simple for operation and safe. To accomplish those operation, an appropriate tool with the projected area less than 1.2 m~2 had been developed by an integrated design approach. It meets the requirement of on-site condition and is good for preserving these existing devices. Through this study and application, the reactor fuel assembly has been disintegrated based on this technique under water in the depth of 6 m.