A heat-dissipating module includes a heat sink and a fan device. The fan device may be disposed on the heat sink, or inserted into the heat sink to reduce the height. The fan device includes a first rotor blade and a second rotor blade. The first rotor blade and the second rotor blade are connected in series. The rotation speed of the first rotor blade is controlled by a first control circuit, and the second rotor blade is controlled by the second circuit. Thus, the second control circuit increases the rotation speed of the second rotor blades when the first rotor blades is failed.