In order to analyze the inner flow pressure fluctuation performance in screw type centrifugal pumps, a ZJ200-25 screw type centrifugal pump with double screw blades was chosen as the study subject. Based on Navier-Stokes equations and shear stress transport (SST) turbulent models, 3-D unsteady flow field of the pump was simulated numerically under several operating conditions. Seven monitor points were set at the impeller-volute coupling interface, inlet and outlet faces of the pump. The pressure fluctuation and the corresponding frequency spectrum at different monitor points were obtained from the simulation. The simulation results showed that the pressure fluctuation in the pump was periodical at different operating flow rates. The impeller blade passing frequency and impeller rotational frequency were the dominant frequency at different positions, where the dominant frequency of the impeller-volute coupling interface was nearly equal to the impeller rotational frequency, and that at the inlet and outlet face were nearly equal to the impeller blade passing frequency. The amplitudes of the pressure fluctuation at the inlet and outlet were lower than that of the impeller-volute coupling interface, and the highfrequency components at the inlet and outlet were fewer than that of the impeller-volute coupling interface. The dominant frequency at the same monitor point was constant but with different amplitude at different operating conditions, the pressure fluctuation at the coupling interface had a lower strength at the position where far away from the volute tongue.