Abstract: Disclosed is a backup heat-dissipating system having a serial fan which can be assembled easily, fastly and conveniently, and can effectively eliminate the interference between fans and prevent the air leakage resulting from the failed fan unit. The backup heat-dissipating system includes a main frame, a first rotor device disposed in the main frame and including a first control device, and a second rotor device disposed in the main frame to be coupled with the first rotor device in series along an axial direction of the main frame and including a second control device. When the first rotor device is failed, the first control device will output a signal to the second control device for driving the second rotor device to rotate at a relatively higher speed.