The utility model discloses a motor driving system and a new energy automobile. A motor driving system comprises a main power supply, an auxiliary power supply, a step-down circuit, a three-phase full-bridge circuit and a motor. Wherein the three-phase full-bridge circuit is connected with and drives the motor, two poles of the auxiliary power supply are respectively connected with two input endsof the three-phase full-bridge circuit, and the main power supply is connected in parallel with the auxiliary power supply through the step-down circuit; in the starting stage of the motor driving system, the auxiliary power supply provides power required by the motor driving system, after the motor driving system operates stably, the main power supply and the voltage reduction circuit work, and the main power supply provides power for stable operation of the motor driving system. According to the utility model, through mutual cooperation between the auxiliary power supply and the main power supply, the auxiliary power supply provides instantaneous high-power energy in a system starting stage, the service life of the main power supply can be effectively prolonged, the power supply efficiency is improved, and through adding the voltage reduction circuit, the voltage levels of the main power supply and the auxiliary power supply can be conveniently matched, and the application is convenient.