A cooling-fan-free system module includes a housing unit having a front and a rear case together defining a receiving space therebetween, and the rear case being highly thermal-conductive; a circuit module received in the receiving space of the housing unit and including a circuit board having at least one heat-producing element electrically connected thereto; a heat radiating unit including a heat-conducting pad raised from an inner side of the rear case corresponding to the heat-producing element for transferring heat produced by the heat-producing element to the rear case, and at least one fin-like heat radiating member integrally formed on a back side of the rear case; and a tightening unit including at least two sets of internally threaded posts, screw fasteners, and elastic elements to ensure tight and good contact of the heat-conducting pad with the heat-producing element.