The application of nondestructive evaluation to creep-fatigue damage was examined in this paper. Generally, as the hold time of static load increases, the degradation of material becomes more rapid and the creep-fatigue life decreases. Therefore, in the evaluation of creep-fatigue strength and life of high-pressure vessel such as main steam pipe at high temperature is very important in power plants. In this study, the creep-fatigue behavior of P92 steel was evaluated nondestructively by the backscattered ultrasound using the creep-fatigue specimens. The results obtained by Rayleigh surface wave of backscattered ultrasound were compared and analyzed with the experimental parameters. Also, the relation between the SDA (slope of degraded area) and creep-fatigue life was examined. From the result of nondestructive test, we suggest that SDA would be used as the new parameter for the evaluation of creep-fatigue damage. As the degradation increased, the SDA decreased and also the creep-fatigue life decreased.