In the present study, the effects of the design factors and operating conditions on flow characteristics of a vane pump for the automotive power steering system has been analyzed numerically. An unsteady moving mesh technique with cell expansion/contraction method is used to simulate the rotation of vanes with respect to stationary inlet and outlet. As a result, the flow characteristics of the flow rate and pressure rise across the vane pump were obtained. The numerical analyses for the various design factors such as number of vanes and thickness between the rotor and camring and for various operating conditions such as rotational speed and pressure difference between inlet and outlet were extensively performed. And the results were discussed in the paper.