An exemplary server system includes a server cabinet defining a space therein; a number of racks arranged in the space, a number of servers mounted in the racks, and a heat dissipation apparatus arranged under the racks. A channel is defined between the racks. Each of the servers includes a drawing fan. The heat dissipation apparatus includes a fan module and two heat exchangers respectively arranged at opposite sides of the fan module. The fan module is aligned with the channel for generating upward a flow of cooling air upward to the channel. During operation of the server system, the cooling air is drawn across the servers by the drawing fans to evacuate heat from the servers and becomes heated air, and the heated air flows down to the heat exchangers where the heat is dissipated from the heated air such that the heated air become the cooling air again.