Modified 9Cr-1Mo steel (P91 steel) with excellent creep strength and corrosion resistance is used for main high-temperature equipment such as boilers and high-temperature piping of ultra-supercritical thermal power plants [1]. This equipment has geometric discontinuities and is subjected to creep-fatigue loading, which is a superposition of creep and fatigue, during start-up, steady operation, and shutdown of the equipment. Therefore, predicting the crack initiation life at the stress concentration site under creep-fatigue loading is one of the important issues in high-temperature strength problems. In this study, we performed inelastic finite element analysis of circumferentially notched specimens with different radii using finite element analysis software developed by our group [2] and attempted to estimate the hysteresis loop and crack initiation life. To verify the validity of the FE results obtained, we compared them with the results of creep fatigue tests conducted separately by us. As a result, it was confirmed that the hysteresis loop, the change in peak stress with the number of cycles, and the stress relaxation curve were in good agreement with the test results. We also performed a simulation of crack initiation and propagation at the notch root by incorporating a non-localized scheme. As a result, it was also confirmed that the cross-sectional observation results were in good agreement with the simulation results, and the crack initiation life at the notch root could be predicted within a factor of two