An LED heat-conducting substrate and its thermal module wherein the composite heat-conducting substrate is incorporated by multiple heat-conducting wires or fibers and insulating material. Said wires or fibers are arranged at interval, and penetrate the front and rear faces. The wires or fibers are segregated by insulating material. An electrode pad is incorporated onto the front face of the composite heat-conducting substrate, and is electrically connected with the electrode pin of LED unit. A heat-conducting pad is incorporated and kept in contact with the heat sink of the LED component for heat conduction. An insulating layer is incorporated onto the rear face of the composite heat-conducting substrate, and located correspondingly to the electrode pad. The LED heat-conducting substrate and thermal module can be constructed easily for high heat conduction in the thickness direction and high electrical insulation in the direction of plane, enabling quick heat transfer to the heat-sinking component.