This paper shows the procedures and results of finite element analysis about NPP HP rotor to assess integrity and determine critical crack size. Heat transfer analysis and stress analysis were performed for cold start and normal operating conditions. Stress intensity factors were calculated for various crack size. Material properties were taken from references such as ASME B&PV Code Section III Part D, EPRI technical reports, ASTM STP. Critical crack size were determined compared to material properties such that brittle fracture occurs or SCC growth rate increases rapidly.