Abstract: The vibration phenomenon of 100D main pump under various operation modes for CPR1000 unit show that, when the main pump motor is in normal shutdown condition of steam generator cooling or residual heat removal cooling, the amplitude value of the main pump motor tile often has a large range of impact fluctuation or even triggers high vibration alarm. According to the principle of mechanical vibration, the frequency-domain and time-domain characteristics of motor bearing vibration and main pump shaft displacement signals are comprehensively analyzed. The vibration amplitude fluctuation is affected by the low-frequency random vibration of about 7~9 Hz. The signal collected by the vibration and noise monitoring system is used to analyze the low frequency vibration corresponding to the core basket beam vibration induced by the main coolant flow in the primary circuit. According to the theory of fluid induced vibration, the main factors affecting the vibration fluctuation of the main pump motor are analyzed and verified by the historical operation records of the main pump. The suggestion of optimizing the operation strategy of CPR1000 unit to alleviate the vibration fluctuation of main pump motor is put forward systematically, which provides a reference for the safe and stable operation of the main pump.