Detailed flow characteristics in the impeller side chamber of a centrifugal pump were studied using CFD method. The computational domain was made up of impeller passages, volute casing, impeller side chamber and seal clearance. Under the hypothesis of steady flow, the RNG k-εturbulence model and RANS equations in multiple reference frames were used to simulate the flow fields. The good agreement of computational and experimental data shows that the CFD method is appropriate for the present study. Computational results reveal that the flow fields are unaxisymmetric in the impeller side chamber, and much more complex than that in an enclosed rotor-tator system. Nevertheless, along axial direction, the velocity profiles are similar with each other both in the impeller side chamber and in the enclosed rotor-stator system.