Abstract: The control rod drive mechanism (CRDM) housing of nuclear power plant is installed on the reactor pressure vessel head by welding and interference fit. This structure improves the performance of the equipment, and ensures the plant steady operation. The theories of the interference fit were discussed. By using of the ANSYS software procedure’s methods, the interference fit was calculated, and the error was analyzed. The methods of interference fit analysis and their advantages were described in detail, and the basis for equipment stress analysis and the design optimization was provided.