Abstract: A finite element model of a SAF2205 duplex stainless steel cruciform joint was established. The temperature field and residual stress field during the welding process were simulated by the thermo-mechanical coupling method and were introduced as predefined fields. High-cycle fatigue behaviors under different stress levels were conducted by ideal elastoplastic model, isotropic hardening model, and mixed hardening model, respectively. The influence of hardening behavior on the evolution of residual stresses during the fatigue process was studied. The results show that residual stress relaxation occurred within the cruciform joint after the first cycle for all models. The most significant residual stress release and the most pronounced relaxation behavior were observed with the ideal elastoplastic model, followed by the isotropic hardening model, while the least release was identified with the mixed hardening model. The unreleased residual stress accelerated fatigue damage by increasing the mean stress of the fatigue load, whereas the released residual stress was converted into plastic strain, altering the deformation characteristics of the material by raising the mean strain.