In order to research pressure fluctuation of unsteady flow in screw-type centrifugal pump with small blade, three-dimensional unsteady flow field of the pump was simulated numerically to the screw-type centrifugal pump with and without small blade based on Navier—Stokes equations and k-εturbulent model. Pressure fluctuations in the outlet of pump and in the volute were obtained at different flow rates. The analysis results indicated that the pressure wave in the pump was always periodic in the two models, and impeller blade passing frequency was the dominant frequency. Compared with the result of single blade at different flow rates, the period decreased to half, and the amplitudes of pressure fluctuations in the pump was smaller, the high-frequency components were also fewer. The analysis results indicate that the adding of small blade in impeller of screw-type centrifugal pump with single blade can not only decrease the pressure fluctuation of unsteady flow in the pump, but also decrease oscillations in volute.