Abstract: The abnormal vibration phenomenon was discovered by monitoring the state of the 2# fan located in the nuclear workshop in Unit 1 of Fangchenggang Nuclear Power Plant. In order to capture the specific fault frequency signal, it is necessary to optimize the vibration data collection definition according to the fan structure style. The spectral analysis and failure diagnosis found that the existence of beat vibration is the reason that the motor vibration exceeds the standard. The several potential equipment defects were identified successfully. According to the diagnostic results, an exact treatment scheme was provided as a preventive maintenance. It effectively reduced the vibration level, and ensured the healthy and stable operation of the equipment.