The invention provides a heat-dissipation device and a heat-dissipation method thereof. The electronic device includes a heat source, a thermal interface material (TIM) in contact with the heat source, a heat-dissipation module in contact with the thermal interface material, and an elastic member pushing the heat-dissipation module toward the heat source. The elastic member includes a base and a compressible portion extending from the base, whereby a force, applied to the compressible portion, is transmitted to and uniformly distributed on the base. The heat-dissipation method includes the steps of overlapping a thermal interface material and a heat-dissipation module on the heat source, and exerting a force toward the heat source to the heat-dissipation module.