The hydraulic performance analysis of a turbopump with an inducer for a liquid rocket engine was performed using three-dimensional Navier-Stokes equations. A simple mixing-plane method and a full interaction method were used to simulate inducer/impeller interaction. Two methods show almost similar results due to the weak interaction between the inducer and impeller since the inducer outlet blade angle is lather small. But, when the inducer and the impeller are closely spaced near the shroud region, flow angles at the impeller inlet show different results between two methods. Thus, the full interaction method predicts about $2\%$ higher pump performance than the mixing-plane method. And the effects of prewhirl at the impeller inlet are also investigated. As the inlet flow angle is increased, the head rise and the efficiency are decreased. The computational results are compared with measured ones. The computational results at the design point show good agreements with experimental data, however under-predicts the head rise at high mass flow rates compared to the experiment.