In a vehicle with an internal combustion engine, a coolant is required to cool the engine, and an electric water pump (EWP) circulates the coolant. In this study, the impeller geometry in the module was optimized based on the design of an experimental method to improve the performance of the EWP, and the results were analyzed. Three design variables were selected: the inlet angle, outlet angle, and blade thickness. The analysis results showed that the outlet angle had the largest impact on pump performance, and we confirmed that the larger the outlet angle, the higher the efficiency or lift of the pump. By optimizing the shape of the impeller blade, we observed that the lift increased by 0.89 m and the pump efficiency increased by 2.8%.