Abstract：Yangjiang Nuclear Power Station unit 1 safety injection pump-motor, the motor occurred with high vibration during the trial process. In order to solve the common problem of the motor vibration of the model, the root cause analysis method was used to analyze the motor vibration. The problem of excessive motor vibration was virtually solved by increasing the motor strength, changing the motor stator and rotor clearance, replacing the bearing form, and meanwhile combining with spectral analysis. During the motor design, problems such as insufficient stiffness of motor support plate, inappropriate lectotype of bearing, resonance of rotor has been solved by root cause analysis and the related experimental. This paper described the process and result of the high vibration of motor, and analyzed the root-cause of motor vibration.