A wind-power generation system with an over-speed protection is disclosed. The system is provided to convert wind energy into mechanical energy by a wind turbine, and mechanical energy is converted into electric energy by the wind turbine driving a generator. Also, electric energy is delivered to a power grid. The wind-power generation system mainly includes an AC crowbar, a fuse, and a DC chopper. The AC crowbar or the DC chopper is provided to consume superfluous energy outputted from the generator, thus providing an over-load operation to brake the wind turbine when the wind turbine operates under a first stage over-speed operation. Finally, the generator is isolated from the generator-side converter by disconnecting the fuse when the wind turbine operates under a second stage over-speed operation.