Experiment and numerical simulation research were conducted on a designed mixed flow pump with the low specific speed of 148.8. By comparing the mixed-flow pump performances at different flow rates, the numerical results and the test results were in good agreement. Monitoring points in the internal flow field were set to capture the pressure fluctuations from rotor-stator interface to the guide vane exit in both the experiment and the numerical simulation. Through analyzing the pressure fluctuations of mixed flow pump at the different flow rates, the pressure fluctuations in guide vane were mainly affected by impeller rotation, and the frequency was impeller blade frequency. From rotor-stator interface to the guide vane exit, the average pressure was increased gradually, and the amplitude of pressure fluctuations gradually became weaker. At the off-design points, the pressure fluctuations became more complex. At low flow rate, there were many low frequencies of the vortex fluctuation with low amplitude, which was consistent with flow field in the test. At high flow rate, the main frequency was also the impeller blade frequency, and there were some low frequencies of the vortex fluctuation with low amplitude, which were better than the low flow rate. These results can be useful for further optimization design of mixed flow pump.