Abstract: Creep-fatigue test was conducted on P92 steel at 625℃. The effects of strain amplitude (0.4%-1.4%) and holding time (30-300 s) on cyclic deformation behavior of P92 steel were analyzed, and micro-mechanism under creep-fatigue interaction was discussed and compared by low-cycle fatigue tests. The results show that creep-fatigue interaction caused the transformation from non-Masing property to Masing property of P92 steel, and stress relaxation during holding time led to accelerated cyclic softening under creep-fatigue loading. During fatigue process, the microstructure of P92 steel changed inhomogeneously, the dislocation density decreased, and finally an elongated subgrain structure was formed. During creep-fatigue process, the microstructure change and dislocation density decrease of P92 steel were more uniform and significant, and finally equiaxed subgrains or dislocation cell structures were formed, accompanied by the coarsening of precipitates.