The invention discloses a cooling system of a fan clutch. The cooling system comprises a driving shaft, wherein a driving disc is fixedly connected onto the driving shaft. The right side of the driving disc is provided with a cover body, and the left side of the driving disc is provided with a shell body. Two oil return channels are symmetrically arranged on the cover body, and the axis of each oil return channel is vertical to the axis of the driving shaft. Two oil return holes are also arranged in the cover body, and each oil return hole and each oil return channel are respectively and correspondingly arranged and are communicated with each other. As the two oil return channels are symmetrically arranged on the cover body, the dynamic unbalance of the clutch is reduced. The axes of the oil return channels are adjusted to be vertical to the axis of the driving shaft, so that a machining technology of the oil return holes of the clutch is greatly simplified, and the machining cost is reduced. The axis size of the driving disc and the cover body is compressed, so that the space volume of the clutch is reduced by about 10 percent, the radial clearance of annular grooves between the driving disc and the shell body as well as the cover body is reduced, and the capacity to transfer torque of the clutch is increased.