The stress and deformation of centrifugal pump impeller have certain impacts on the velocity and pressure fields. A solution for the flow field of centrifugal combined with structure response of impeller was implemented by using two-way coupling method to investigate the effect of FSI of impeller on flow field. By using this method, various flow rate conditions were calculated. The results showed that the stress of the impeller was markedly uneven and the local stress concentration appeared in each operation condition. The back cover board of impeller outlet had large deformation deviating from the design value, which affected the impeller velocity, made the shunt parts in the volute to move export, led to severe unsymmetry phenomena and instability of pressure in impeller outlet. Pressure of every monitoring point changed obviously.