The sequential-coupled thermo-mechanical model and direct cyclic technique are employed to investigate laser welding and low-cycle fatigue residual stress, respectively. The effects of residual stress on fatigue properties and the relaxation behaviour are analyzed. The simulation results highlight the strong dependence of laser welding residual stress on constitutive models and how low-cycle fatigue residual stress is influenced by the initial laser welding residual stress. Furthermore, the simulation indicates that residual stress redistributes and relaxes in the weld and heat-affected zone after low-cycle fatigue. To validate the accuracy of the simulation, the neutron diffraction experiment is carried out, and the experimental data are consistent with the simulation results.