A heat dissipation device includes a heat sink defining a pair of cutouts at two opposite sides thereof. The heat sink includes two pads fixed in the cutouts, respectively. Each pad defines a slot therein. A retention module supports the heat sink thereon, and extends a pair of clamping arms in the cutouts of the heat sink. Each clamping arm defines a slit. A clip includes two abutting portions rotatablely connecting with the pads and the clamping arms, and two pressing portions slidably received in the slots of the pads and the slits of the clamping arms. When the clip is moved to a locked position, the pressing portions of the clip press the pads downwardly a distance relative to the clamping arms so that the heat sink can have an intimate contact with an electronic device.