Abstract: Creep-fatigue tests under stress control and strain control were conducted on P92 steel at 600 ℃. The effects of load level and load holding time on the creep-fatigue damage were analyzed. By combination of stress controlled creep-fatigue test data, introducing the modified Chaboche nonlinear follow-up hardening rate and creep strain under the framework of viscoplastic unified constitutive theory, and considering the damage evolution law, the coupled creep-fatigue damage constitutive model based on Chaboche theory was established. The creep-fatigue cyclic curves of P92 steel were simulated. The results show that P92 steel exhibited cyclic softening characteristics at 600 ℃. Under stress control, the damage of P92 steel at high load holding was positively correlated with the average stress, while the damage at low load holding was negatively correlated with the average stress. Under strain control, P92 steel showed stress relaxation behavior, and the longer the load holding time, the more obvious the stress relaxation. The established creep-fatigue damage constitutive model could simulate the cyclic characteristics of P92 steel well, and the maximum relative error of the stress simulation in creep-fatigue process was 7.30%.