In additive manufacturing (AM),numerous thermal cycles make stress relaxation a significant factor in affecting the material mechanical response.However,the traditional material constitutive model can-not describe repeated annealing behavior.Here,we propose an improved constitutive model based on a serial of stress relaxation experiments,which can descript the temperature and time-dependent stress relaxation behavior during AM.By using the proposed relaxation model,the prediction accuracy is sig-nificantly improved due to the recovery of inelastic strain during multilayer deposition.The results are validated by both in-situ and final distortion measurements.The influence mechanism of the relaxation behavior on material mechanical response is explained by the three-bar model in thermo-elastic-plastic theory.The relaxation behavior during the whole AM process is clarified.The stress behavior is found to have a limited effect when merely depositing several layers;nevertheless,it becomes a prominent impact when depositing multiple layers.The proposed model can enhance modeling accuracy both in AM and in multilayer welding.