A power module includes a power source module and a metallic heat-dissipation substrate. The power source module has an input pin and an output pin soldered on and electrically connected with a system board and includes a printed circuit board. The printed circuit board has a first surface and a second surface. At least a heat-generating component is disposed on the second surface. The metallic heat-dissipation substrate has a first surface and a second surface opposite to each other. The first surface has at least a fixing position and at least a heat-dissipating position. The fixing position is directly or indirectly connected with the second surface. A gap accumulated by tolerances is existed between the heat-dissipating position and the heat-generating component. A gap-filling material is filled into the gap. The second surface and the system board are soldered with each other. Therefore, the heat-dissipation efficiency is enhanced.