Abstract: The welding residual stress is the main cause of the stress corrosion cracking. The accurate determination of the residual stress distribution in the soldering seam of the structure is the key step to assess the structure integrity. In this paper, two penetration prototypes of the control rod drive mechanism (CRDM) are manufactured using the same processing technique and design method of the real CRDM penetration product, and the blind-hole method is selected to test the welding residual stress of the two J-shaped welds, in order to explore the residual stress distribution of J-shaped welds in the penetrations of the control rod drive mechanism in the reactor pressure vessel closure head. Experimental analysis has determined the residual stress distribution of J-shaped welds of CRDM penetrations in the reactor pressure vessel closure head, which can provide the necessary reference for the study of the structure integrity of reactor pressure vessels.