Abstract: The blade of impeller, which is complicated spatial curved volume, directly influences on its hydraulic performance and running stability. Basing on the flow law of liquid, flow superposition design for the impeller of engine water pump was applied following to the flow trail. The flow of liquid in water pump was considered as the superposition of axial and radial flow at motionless and the peripheral flow at rotating, so its meridian contour and blade type could be designed with corner flow law and source-vortex flow law. According to the computational fluid dynamics (CFD)  simulation result, this method can avoid uneven pressure because of uneven spatial liquid flowing, and reduce back flow and secondary flow, accordingly reduce energy loss and increase pump efficiency.