In order to obtain the accurate characteristics of pressure fluctuation in the axial flow pump, the monitoring points of pressure were set near the impeller inlet, the blade passages and the vane outlet. The test was conducted by applying the high precision digital pressure acquisition system under 4 different flow rates which are 0.45, 0.8, 1.0 and 1.2 of the design flow(Qd), respectively. Time domains of pressure fluctuations show that: under stable conditions (0.8Qd, 1.0Qd, 1.2Qd), the pressure at P1 near the inlet shows a regular waveform with 3 peaks and 3 valleys as time changes, which is associated with the blade number. Due to the interaction between the rotor and stator, the pressure at both P2 and P3 inside the vane shows a second harmonic wave with a lower amplitude. While at 0.45Qd, the pressure of 3 points show a significant second harmonic wave due to the drop of head. Based on Fast Fourier Transform(FFT), the main frequency of all monitors is always the blade passing frequency(BPF) with its amplitude decreasing from the impeller inlet to the vane outlet under stable conditions. However, the unsteady flow like backflow and tip vortex at 0.45Qd lead to the complex frequency components and the main frequency shifted to high frequency segment accompanied by higher amplitude.