A thermal module includes a fixing rack and a heat sink fitted in the fixing rack. The fixing rack is provided at an inner side with a plurality of stoppers and a plurality of projected portions located adjacent to the stoppers with a height difference existed between them. The heat sink is provided along an outer periphery with a plurality of vertically extended grooves. The heat sink may be selectively fitted in the fixing rack with the grooves corresponding to or not corresponding to the projected portions on the fixing rack, so that an upper surface of the heat sink may be upward abutted on the upper stoppers or the projected portions, respectively, to restrict the fixing rack from sliding downward. Meanwhile, due to the height difference between the stoppers and the projected portions, a distance between the upper surface of the heat sink and the fixing rack is adjustable.