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In order to study the mechanism of bottom vortex generation in the suction passage of pumping station, and explore the relationship between pressure pulsation and vortex generation under flare pipe at bottom of suction passage, 20 pressure pulsation monitoring points were evenly arranged at the bottom of suction passage in the form of concentric circular ring. At speed of 2200r/min, the pressure pulsations experiment under different flow conditions was done. By analyzing the time domain and frequency domain of pressure fluctuation and pressure distribution at the bottom of suction passage, the law of pressure pulsation at the bottom of suction passage of the axial flow pump was revealed. According to the analysis of pressure fluctuation time domain, the pressure fluctuation amplitude of the bottom water flow at the bottom of inlet basin was decreased and then increased with the increase of flow rate. The maximum pressure of the flow pressure was fluctuated under the large flow condition, which was the same as the design flow. No vortex and whirlpool occurred mainly in the case of large flow conditions. The experimental results showed that the pressure pulsation at the bottom of the suction passage was twice as high as that of the impeller, and there was no dominant frequency at impeller frequency, which indicated that the pressure pulsation at the bottom of the suction passage under the bell-tube of the axial flow pump was still affected by impeller rotation. Under large flow conditions, the vortex under the bell-tube was easy to produce with high frequency of occurrence and long duration. The position of the vortex under different working conditions was corresponded to the position of the low pressure zone at the bottom of suction below the bell-tube.