Abstract: The residual heat removal pump is a nuclear secondary pump, guarantying the safe shutdown of the nuclear power plant. The combination of vaned diffuser and annual volute is applied to ensure the safe and stable operation of residual heat removal pump. In order to investigate the distribution and transportation of pressure fluctuations induced by rotor-stator interaction in a centrifugal pump with vaned diffuser, the pressure signals obtained by numerical simulation and experiment were analyzed with spectral method. The results show that the numerical performance and frequency domain of monitors on volute have a good agreement with the experimental ones. The distribution of spectral amplitude of pressure fluctuation at vane pass frequency and its high harmonic frequencies increases from impeller inlet to outlet, reaching the highest value at the pressure side of trailing edge. The spectral amplitude of pressure fluctuation at blade pass frequency is the strongest in the throat area of diffuser, achieving the highest value at the leading edge of diffuser vane. The distribution of spectral amplitude of pressure fluctuation in volute is relative to the diffuser position. The frequency components of pressure fluctuations induced by rotor stator interaction consist of two fundamental frequencies, namely blade pass frequency and vane pass frequency. The results can provide meaningful reference to decrease the pressure fluctuations in centrifugal pump.