In order to analyze the effect of fluid-structure interaction (FSI) on flow field in screw centrifugal pump, a ZJ200—25 screw type centrifugal pump with double screw blades was chosen as the study subject. The two-way coupling method was established to study the effect of FSI of impeller on flow field in screw centrifugal pump. CFX12.1 and ANSYS Workbench were used to the combined calculation for turbulent flow and structure response of impeller. And the unsteady flow field of the pump was simulated numerically under several operating conditions without effect of FSI. Compared the result of the two calculation methods, it’s found that, with the effect of FSI, pressure fluctuations in pump inlet intensified. The dominant frequency of pressure in inlet and outlet do not change but the phase position was different after FSI. The inner velocity distributions satisfy the common characteristic, but the largest differences were appeared under the condition of small flow rate. The flow field near volute tongue was affected by FSI most obviously when blades passing by the tongue. Magnitude of radial trust changing with time has similar regularities, but the fluctuation range with FSI method was reduced. Flow filed in impeller was more dissymmetrical under the effect of fluid-structure interaction. The conclusion obtained in this investigation will provide an essential guide to analyze the inner flow filed and master characteristics of rotor vibration characters and inducing factors of the pressure fluctuation in the screw type centrifugal pump.