Due to the high vibration of the lower rolling bearing of circulating seawater pump in a CPR1000 Nuclear power unit， there is a risk of emergency load reduction or shutdown. It is of great significance to carry out vibration fault diagnosis and trend analysis. By analyzing the signal and root mean square signal of vibration velocity of the BCV 285 circulating seawater pump in operation， it is found that the local spalling exists in the outer ring raceway of the bearing， and the resonance is the main reason for the high vibration defect of the seawater pump. The resonace of the seawater pump is reduced by strengthening the lubrication of the bearing and the rigidity of the foundation. The practice shows that the real-time monitoring of the root mean square value of vibration velocity can guide the safe operation of the circulating seawater pump effectively.