Abstract: In order to investigate the pressure fluctuation induced by the rotor-stator interactions of the mixed-flow pump, the standard turbulent k-ε model and SIMPLEC algorithm were applied to simulate the unsteady flow in a high-specific-speed mixed-flow pump. The pressure fluctuations at four representative locations under multi-conditions were obtained, and the time-domain and frequency-domain of each monitoring point were analyzed. Comparison of calculated steady flow head and efficiency with the test results verified that the inner flow characteristic simulated by this calculation method was comparatively accurate. The numerical results showed that the maximum pressure fluctuation appeared at impeller inlet where the pressure coefficient amplitude increased gradually from hub to rim; the fluctuation at impeller inlet became stronger with the deviation of flow rate from design point and the relative fluctuation at 0.7Qopt was about 0.5 time stronger than that at the design flow rate. The frequency domain transformed by Fast Fourier Transform (FFT) showed that the dominant frequency was approximate to the blade passing frequency. The numerical results can provide certain theoretical references to reveal the pressure fluctuation in the mixed-flow pump.