Abstract: The plastic behavior of 13MnNiMoR steel under cyclic load was studied by low cyclic fatigue tests at different temperatures (20-800 ℃). The material constants of hardening model at different temperatures were obtained by fitting the low cyclic fatigue test data. The residual stress in butt girth welding of ultra-thick 13MnNiMoR steel cylinder was simulated by mixed hardening, isotropic hardening and kinematic hardening models, and compared. The simulated results were compared with the results measured by X-ray diffraction. The results show that the 13MnNiMoR steel was a cyclic softening material. The difference in prediction for hoop residual stress by different hardening models was greater than that for axial residual stress, and the difference in prediction for residual stress on inner surface was bigger than that for residual stress on outer surface. The isotropic hardening model overestimated the residual stress, while the kinematic hardening model underestimated it. The welding residual stress predicted by the mixed hardening model was the most close to the test values by X-ray diffraction, indicating that the mixed hardening model can predict multi-layer and multi-pass welding residual stress of ultra-thick plate.