Hub motor is the core component of new energy vehicle, its efficiency and stability play a decisive role in the quality of the vehicle. The working space of in-wheel motor is compact, and the temperature rise directly determines it’s the working efficiency and life. Therefore, it is very important to study the cooling mode of hub motor. Taking 75 kW outer rotor hub motor as an example, the loss, heating and cooling of hub motor for electric vehicle are studied and analyzed. The stator core loss, permanent magnet eddy current loss and winding copper loss of the motor are calculated. 3D finite element models of temperature field of hub motor with natural cooling and water cooling are established respectively. Based on the model, the temperature distribution of each part of hub motor under different cooling modes was calculated and obtained. By changing the flow rate of cooling water, the temperature rise curves of each component at different flow rates are obtained, and the best cooling scheme is finally selected.