Swing check valve used in nuclear power equipment is prone to crack and wear during service,which seriously affects the safe operation of the equipment. In this paper, Fluent is used to find out the location where defects are likely to occur during the stable operation of swing check valve,and the defect location is extracted. The numerical simulation of digging repair welding process is carried out by Inte Weld. The value and distribution of residual stress and strain in the weld under different welding powers are studied.The calculation results show that the bottom of the check valve is most likely to be damaged. The welding residual stress reduces as the welding power decreases. The welding sequence is that the residual stress from both sides to the middle is greater than that from left to right. The residual stress reduces as the cooling time between passes increases. When the welding power is 2400 W,the welding sequence of each layer is from left to right,and the cooling time between each weld is 300 s,the value of the residual stress in WCB repair welding is the minimum,which is 323 MPa. The deformation can be improved when the welding sequence of each layer is adjusted to alternately from left to right and right to left.