A heat sink includes a cooling module and an installing assembly for fixing the heat sink on a housing. The installing assembly includes a case, a handle rotatablely fixed in the case and a support including a fixing board with blocks and two brackets. The handle is actively connected with the support. The fixing board is fixed on a bottom plate of the case. The handle includes two bulges. The brackets include two slide openings for receiving the bulges. When the heat sink is installed, the handle is rotated to be vertical, the bulges are out of the slide openings, and the blocks are stuck on the housing. When the heat sink is dismantled, the handle is rotated to be horizontal and the bulges are stuck into the slide openings to resist the brackets, thereof the fixing board being uplifted and the blocks being pushed away from the housing.