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The pressure pulsation is one of the main causes of vibration and noise in axial flow pump, in order to study the mechanism of pressure fluctuation induced by vortex, several pressure pulsation monitoring points were stalled at the bottom of the pump sump, the horn mouth, the impeller inlet and outlet, the outlet of the guide vane. The flow rate of 1.2Qd (1.2Qd=38.4L/s) was selected. The dynamic process of vortex generation and disappearance was measured by an advanced high-speed camera, and the microscopic variation of the vortex was observed. The results showed that the vortex tube below the horn position and low position, the maximum amplitude of pressure fluctuation at the bottom of the vortex tube, the Cp value was about 1.8~2 times of the non center point of pressure fluctuation of Cp value, at the center of tube, the pressure pulsation frequency of the vortex occurred at 1 time of the impeller rotation frequency. The pressure fluctuation at the impeller inlet and the pressure fluctuation at the impeller were synchronized at 1 time of the impeller frequency, and the pressure pulsation frequency was 1 time of the frequency of impeller. The detailed structure of the vortex changes was clearly observed by high-speed cameras. On the whole, the maximum amplitude of pressure fluctuation was at the inlet of impeller, and the maximum amplitude of pressure fluctuation occurred at the center of the vortex belt. The Cp value of the pressure fluctuation at the center of the vortex belt was about 1.8~2 times of the Cp value of the pressure fluctuation at the non center point. Getting through the water inlet swirl from generation to the collapse process and the influence of pressure fluctuation, can provide a theoretical basis for the pumping station project of vortex elimination measures.