In order to evaluate the impregnating resin for driving motor of new energy vehicles, epoxy resin and polyester imide resin were selected as research objects. The properties of the two impregnating resins were compared by thermal weight loss and bonding strength tests, and their long-term ageing characteristics were compared emphatically. The results show that the VOC content and long-term thermal resistance of the two impregnating resins meet the requirements. The bonding strength of epoxy resin is higher than that of polyester imide at 25℃, but decreases rapidly at 150℃ and 180℃. Ageing at 200℃ for 2 000 h, high and low temperature impact for 600 cycles, high and low temperature for 8 cycles under ATF oil immersion, high and low temperature for 8 cycles under ATF oil + 0.5% water closed immersion, and ageing at 150℃ for 2 000 h under ATF oil immersion experiments have similar effects on the bonding strength of the two impregnating resins. However, under the condition of ATF oil + 0.5% water closed immersion at 150℃, the bonding strength of epoxy resin is only 16.41%, 13.64%, 4.29%, and 4.29% of the initial value after aged for 500, 1 000, 1 500, and 2 000 h, while the bonding strength of polyester imide is higher than the initial value under the same condition. The structural and elemental changes of epoxy resin before and after its bonding strength decreasing significantly were compared by Fourier transform infrared spectroscopy and X-ray electron spectroscopy, it is inferred that the hydrolysis at high temperature is the main reason for the decline of bonding strength.