Abstract: Using the computational fluid dynamics software Fluent,the three-dimensional turbulent flow of the reactor coolant pump（RCP） impeller at different flow rates and different concentrations of boric acid is simulated.With the experimental data,different effects on RCP performance are analyzed between water and boric acid,especially the influence to the impeller.The feasibility of taking the water as coolant in RCP by using numerical simulation method is analyzed,and the result shows that negligible differences in water and boric acid was acquired even in abnormal concentration of boric acid.It proved that the using of water as coolant when conducting a simulation is feasible.