Abstract: Valve is one of the important control components in the pipeline system of nuclear power plant. In engineering practice, it is found that cracks appear in some valve surfacing layers during operation, resulting in nuclear island pipeline leakage and other major safety accidents. The mechanism of crack formation of Norem 02 iron-bases alloy surfacing layer was analyzed by mechanical load fatigue test and thermal load impact test, and the residual stress of the sealing surface surfacing layer of a nuclear grade valve was calculated by thermal elastoplastic finite element method. The results of numerical simulation were verified by XRD. On this basis, the evolution law of residual stress of surfacing layer under thickness thinning and thermal load was calculated and analyzed. It is found that the cracks in the surfacing layer of the valve sealing surface are brittle penetration cracks caused by the joint action of welding residual stress and thermal stress. During the operation of valve sealing surface, the stress change of surfacing layer caused by the thinning of surfacing layer is very small. Under the action of 1000 ℃ thermal shock load, the stress of surfacing layer increases obviously, and the thermal load is the main factor leading to the damage of the surfacing layer material.