Abstract: Energy storage flywheel mounted in primary circulation pump of the reactor could supply coolant to the reactor core under poweroff accident. The structural integrity of the flywheel has influence on safety of the reactor. Integrity analysis concerned in the structure strength and fracture mechanics of the flywheel was performed using finite element software based on nonlinear contact method. The load cases of interference, rated speed and over-speed were considered. The result shows that stress strength and stress intensity factor at imaginary defect of the flywheel are satisfactory to the requirement of related regulations.