The invention provides a power supply heat dissipation device for a vehicle and a control method thereof. The power supply heat dissipation device comprises a box body; a partition plate for mountinga power supply module is arranged in the box body; the partition plate is transversely arranged in the box body to divide the box body into an upper part and a lower part; the power supply module is arranged on the upper part of the box body; a plurality of cooling fins arranged side by side at equal intervals of the power supply module vertically extend downwards into cooling air ductd on the lower part of the box body; the cooling faces of the cooling fins are parallel to the front-back direction of the vehicle; heat exchange openings are formed in the two sides, in the front-back directionof the vehicle, of the cooling air ducts; and a fan capable of rotating positively and negatively is arranged at the heat exchange opening in at least one side. According to the invention, the heat dissipation efficiency can be effectively improved, so that high-temperature damage to power supply equipment is avoided.