The research was conducted for the purpose of studying the rules of pressure fluctuation under different positions in a centrifugal pump, and to find their relationships. The frequency spectra of pressure signal located at the pump was obtained with CFD. The results showed that the blade passing frequency dominated the pressure fluctuations at the design and large flow rate condition, and at the small flow rate condition the axis frequency became dominative in the pressure fluctuations. The amplitude of the pressure fluctuation was different at the varied flow rates, and the amplitude became higher at inlet and outlet of the passage.