Aiming at the problems of large heat dissipation and high cooling difficulty in the electric drive system of new energy vehicles, this paper designed and developed an oil-water composite motor cooling system based on the Computational Fluid Dynamics (CFD) method. The three-phase quadrupole asynchronous motor was taken as the research object, we analyzed the cooling medium and its flow rate, water jacket structure design and water jacket section area by simulation. The results showed that water is the best cooling medium under the same flow rate and channel structure. When the flow rate of cooling oil is 1.5 m/s and the flow rate of cooling water is 1 m/s, the parameters of the motor are the best. Considering the heat dissipation efficiency and water pressure, the H-shaped channel is more suitable for the actual heat dissipation process of the motor. Similar parameters on the top and bottom of the trapezoidal section of the water jacket can better balance the pressure drop and heat dissipation effect.