Sudden loss of power, the motor in the accident in order to ensure the system safety, motor could drag equipment rely on their own inertia, continue to run 2 minutes. Due to inertia was far less than the system inertia motor itself demand, so need to be on the machine body with large diameter, large flywheel weight, in order to provide enough moment of inertia. In large capacity and high speed vertical motor equipped with big moment of inertia of the flywheel, the stable operation of the motor becomes very important, therefore, shafting on stiffness of the machine itself and the rationality of the structure design should be validated. Aiming at the key points of the motor structure design and calculation, and through the real machine field operation. Verified the reliability of the motor. To provide the reference for electrical engineering application.