A heat dissipation device includes a base, a fin group, a plurality of heat pipes connecting the base and the fin group, a fan cover covering the fin group and a fan located at a side of the fan cover. The heat pipes are received in the base and extend through the fin group. The heat pipes are received in two opposite sides of the fin group and sandwiched between the fan cover and the fin group. The fan cover includes a body and a pair of side walls extending from the body. The side walls each include a plurality of heat-dissipating fins formed on an outer surface thereof for increasing heat dissipating surface of the heat dissipating device.