The cooling effect of oil cooling method on electric vehicle motors with hairpin winding is analyzed. A 160 kW motor being developed by a commercial vehicle company is applied. Firstly, the flow field of oil was analyzed. In the crown part, 96% of the oil flowed; in the welded part, 90% of the oil flowed. Secondly, an analysis of the heat transfer in the coil and stator was performed. The welded part of the coil exhibited an average temperature 4% higher than that of the crown part. Finally, the parametric study was conducted to understand the effect of the temperature and flow rate of the oil on the temperature distributions of the motor. As the flow rate increases, the maximum temperature decreases. However, there is not a big difference at more than 0.8 LPM/LPM. The results provide important information for understanding the effect of a motor using oil cooling.