A computer system includes a computer case, a cover, and an air duct. The computer case includes a display, a housing connected to the display. A motherboard is attached to the housing, and a fan module. The motherboard includes a heat generating component. A first input opening and an output opening is defined in the cover. The output opening corresponds to the fan module. The air duct is mounted on the heat generating component. A plurality first holes are defined in the air duct corresponding to the heat generating component. The air duct corresponds to the first input opening to guide air to flow to the heat generating component via the first input opening and the plurality of first holes.