Abstract: A mock-up of control rod drive mechanism (CRDM) nozzle on the reactor pressure vessel (RPV) head was manufactured with J-type groove. The temperature during welding and the residual stress were measured. The segmented temperature heat source model and the thermal-mechanical coupling method were adopted to efficiently simulate the welding temperature field and residual stress field, and the simulated results were compared with the experimental ones. Based on the simulated results, the residual stress distribution characteristic in the J-weld was analyzed. The investigated results show that the proposed model and the simulation procedure can efficiently obtain the residual stress field in the J-weld between RPV head and the CRDM nozzle, the simulated results generally agree with the measured ones; the longitudinal stress in the J-weld is greater than the axial stress. The stresses on the outer and inner wall of the nozzle are non-uniform. In addition, the stresses in the weld and the nozzle at the up-hill and down-hill regions are larger than those at the side-hill region.