The weak form of the extended finite element method(XFEM)with the initial stress field was derived, and was used to numerically simulate the crack in a weld-induced residual stress field. A more accurate stress intensity factor(SIF)was obtained with the interaction integral method. Based on this, the variation of SIF of steam generator safety-end dissimilar metal joints with the crack depth in the weld-induced residual stress field was analyzed. The results show that SIF increases first and then decreases with the continuous propagation of the crack inside the welded joint, indicating that the resistance of a material against crack propagation increases first and then decreases. The method of exerting an initial stress field utilizes the advantage of XFEM in simulation of crack propagation, and avoids the repetitive computation induced by grid updating.