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For the study of screw pump internal flow and pressure pulsation characteristics, ICEM-CFD was applied to structure mesh generation for flow components, and the steady and unsteady simulations were carried out by CFX software to get the pump internal flow and the pressure pulsations of the monitoring points. The results are as follows: under 0.8Q condition, there is local high pressure area and whirlpools existing at the junction of the hub and the blade, which gradually decrease and eventually disappear as the flow rate increasing; under the design condition and 12Q condition, the internal pressure and velocity distributions gradually become uniform, the flow is stable and the inflow is smooth. The pressure coefficient fluctuation amplitudes of the inlet and outlet of guide vane are significantly greater than that of the impeller and have obvious peaks and troughs; the pressure pulsation mainly generates in the low frequency region, reduces with a cyclical trend, and its amplitudes are generated at the frequencies that are the whole number multiple of the natural frequency. Among the monitoring points, the pressure pulsation amplitude of the inlet is the largest, and the amplitude of blade rim side is larger than that of the hub side. Pressure fluctuation amplitudes of monitoring points at the outlet are uniform and small. In the whole process of pump operation, the smooth downward flow head curve and power curve are obtained, and there is no saddle area and overload phenomenon occurred. These meet the design requirements. Prediction curves are basically consistent with the experimental curves. It indicates that the numerical simulation is accurate and has certain value for spiral axial flow pump design.