Abstract: Single-period strain controlled creep-fatigue tests were carried out on P92 steel at different temperatures (500-675℃) and strain rates (5×10^-6-1×10^-4 s^-1). The initial cyclic characteristics of the steel under creep-fatigue interaction were studied, and the corresponding constitutive equations were established to describe the cycling process. The results show that at load retention stage there was obvious stress relaxation phenomenon in P92 steel; the stress reduction rate had a small difference at 500-650℃, and increased with strain rate at 675℃; the curves of true stress and stress relaxation with holding time simulated by stress relaxation model derived from the power function were in good agreement with test results except the condition of 675℃, 1×10^-5 s^-1, and the relative error was less than 4.28%. At loading and unloading stage, when the strain rate was the same and the temperature was not higher than 550℃, the effect of temperature on stress change rate could be ignored; when the temperature was higher than 550℃, the effect of temperature was great; when the temperature was the same, the effect of strain rate was insignificant. The true stress-strain curve and true stress-time curve simulated by Ramberg-Ostgood model were in good agreement with the test results, and the relative error was less than 10.37%.