A heat sink mechanism includes a fixed and a movable clamping piece, at least one adjusting gearwheel rotatably mounted to and between the fixed and the movable clamping piece via a fixing shaft while an end of the fixing shaft is screwed to the movable clamping piece, and an adjusting worm shaft rotatably mounted to the fixed clamping piece for driving the adjusting gearwheel to rotate via meshed worm threads on the worm shaft and gear teeth on the adjusting gearwheel. When the adjusting worm shaft is rotated, the meshed worm threads and gear teeth bring the adjusting gearwheel and the fixing shaft thereof to rotate, so that the movable clamping piece screwed to the rotating fixing shaft is brought to move toward or away from the fixed clamping piece to thereby fix the heat sink mechanism to a heat-producing source to achieve the purpose of heat dissipation.