With the Abaqus finite element method, the residual stress of DP600 steel after laser welding and low-cycle fatigue is simulated. Due to the large temperature gradient during laser welding and the cyclic loading during low-cycle fatigue, the material produces plastic deformation and strain hardening, in which strain is one of the main parameters affecting strain hardening. This paper first establishes plastic material constitutive models to simulate the laser welding residual stress. Then, low-cycle fatigue residual stress is simulated by the combined hardening models. Finally, the variability of residual stress is analyzed. The results show that residual stress is redistributed and relaxes after low-cycle fatigue. Furthermore, the simulation results are verified by experimental data.