In recent years, better solution solving for both energy and global warming problems have been demanded. For this reason, it would be necessary to continue operating power generation facilities, for a short period of time, under the introduction of natural energy. Combining two different energy systems poses another serious mechanical problem for the main high-temperature components of the power plant. The problem is accumulation of creep-fatigue damage and cracking due to frequent starting and stopping of the equipment. In this study, a damage-coupled inelastic constitutive equation for P91 steel, which is used in major high-temperature component, was formulated as extending Chaboche-type viscoplastic constitutive model [1] by coupling the damage evolutional equation. In order to implement the extended model in the finite element (FE) analysis software MARC, we adopted the numerical analysis method based on the backward Euler procedure proposed by Kulling [2] et al. The implementation was conducted by making use of the user subroutine of UVSCPL and PLOTV, which was coded in Fortran language. Using the developed program, we attempted to simulate the stress-strain curves and to predict fatigue life under high-temperature fatigue and creep-fatigue loading. As a result, it was confirmed that FE results were in good agreement with the experimental results. REFERENCES [1] Yaguchi M. and Takahashi Y. A viscoplastic constitutive model incorporating dynamic strain aging during cyclic deformation conditions, International Journal of Plasticity, Vol. 16, pp. 241-262, 2000. [2] Kulling E. and Wippler S. Numerical integration and FEM-implementation of a viscoplastic Chaboche-mode with static recovery, Computational Mechanics, Vol. 38, pp. 491-503, 2006.