A cooling structure for a continuous variation transmission system of an all-terrain vehicle which includes a radiator mounted at a front end of the vehicle and under a front body cover, a hood enclosing the radiator, a gearbox having an inlet and an outlet, the inlet being connected with an inlet conduit for drawing outside cool air into the gearbox, the outlet being connected with an exhaust conduit for discharging hot air from the gearbox, wherein the inlet conduit has an inlet end mounted between the hood and the front body cover and shielded by the hood and the front body cover, whereby the cooling structure can effectively prevent water, dirt and dust from entering the gearbox and are simple in construction and easy to assemble and maintain.