The 48 V flat wire winding induction motor is taken as the research object, the influence of oil-passive cooling of the rotor of induction motor on the distribution of temperature field and the thermal equalization effect is studied by using COMSOL software. Three-dimensional electromagnetic field analysis is transformed into two-dimensional analysis on the axial middle plane of the motor to simplify calculation and obtain flux density distribution, the loss value of each part of the motor is calculated. A simplified three-dimensional global simulation model of the motor is established, and the transient thermal analysis of the motor is carried out under the large current condition. The simulation results show that the temperature rising of the air gap, rotor, winding in the passive oil-cooling motor is obviously reduced. Through the temperature rising experiment of air cooling and the passive oil-cooling in the two motors with the same parameters. The experiment results show that, compared with air cooling system, passive oil-cooling system can significantly improve the effect of temperature rising of the rotor and winding in the motor, and raise the output power of the motor, which is an economic and reliable cooling system.