In view of a better study on the internal flow characteristics of centrifugal pumps as the turbine, based on standard k-ε turbulence model and SIMPLEC algorithm, a calculation can be made of the pump and pump turbine under different working conditions by using the flow field simulation software CFX, thus obtaining the external characteristics of the pump and pump turbine under different working conditions, followed by an analysis and comparison of the internal flow laws of pump and pump turbine under design conditions. The results show that the characteristics of the internal flow field change greatly during the pumping process. Under the optimal working condition, the efficiency of the turbine is higher than that of the pump, and the distribution of pressure and velocity in the flow field inside the turbine is more uniform than that of the pump, with the energy in the impeller passage changing greatly. Therefore, CFD technology can be applied for the study on the flow characteristics of pumps as the turbine.