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In order to discuss the characteristics of pressure fluctuation in a scaled axial flow pump at different flow rate conditions, the dynamic pressure fluctuation data of six pressure monitoring points on the pump casing was measured at different flow rates, and the law of pressure fluctuation in impeller was revealed. The experimental results show that waveform of pressure fluctuation at impeller inlet P1 was the normal sine shape, and the peak to peak value of pressure fluctuation at the measuring point P2 in the impeller reached the maximum, and then decreased at monitoring point P1 located in impeller inlet. Time domains of pressure fluctuations in impeller had four peaks and four valleys which were consistent with the impeller blade number, due to the alternating pressure gradient. The secondary flow and tip leakage vortex induced the second harmonic wave significantly at the middle of impeller at small flow rate conditions. Based on Fast Fourier Transform, the main frequencies of pressure fluctuations at three measuring points in the impeller region in different flow rate conditions were all blade passing frequency(BPF), and the harmonic frequency was the multiples of BPF. The amplitudes of harmonic frequency decayed exponentially. However, the low frequency which was induced by the reversed flow and flushing occured in the frequency domain of pressure fluctuations in the guide vane, and the BPF and its harmonics coexisted.