The present invention provides a generator brake system for providing a brake control of a generator. The generator brake system includes a power conversion unit, a sensing unit, and a control unit. The power conversion unit receives an output voltage and an output current, generated from the generator, and the power conversion unit has at least one switch unit. The sensing unit receives the output voltage and the output current to generate a voltage signal and a current signal. The control unit receives the voltage signal and the current signal. When receiving a braking signal, the control unit generates at least one control signal for correspondingly turning on the at least one switch unit, thus braking the generator in a short circuit manner.