Abstract： The axisymmetric high-pressure rotor of a ultra-supercritical steam-turbine was modeled by commercial finite element software Abaqus for assesment of its high temperature strength. The loaded thermomechanical coupling boundary condition, the temperature and stress distributions of the rotor, and the equivalent strain history of key points under cold start-up procedure were analyzed. The fatigue damage of the rotor during a start-up and shut-down cycle was predicted by the Mansoncoffin formula. The results demonstrate that the temperature difference caused by comdensation heat transfer between the surface and center of the rotor is initially large. The rotor is affected more significantly by thermal stress, and uneven heating results in large thermal stress at the initial phase of the start-up procedure, while the stress reduces during the later period of the startup. Furthermore, the maximum fatigue damage occurs on the arc segments of the balance pistons, and the damage value is 1.692×10-4. Consequently, the danger of low-cycle fatigue failure should be ignored in application.