The invention relates to a voltage detection control technology, especially relate to a hardware overvoltage disconnecting circuit wherein a DC power supply module is disconnected from a power network when the AC power network is in the state of overvoltage. The hardware overvoltage disconnecting circuit comprises a disconnecting relay and a voltage detection circuit. The disconnecting relay is connected in series between an AC power network and a power factor correction circuit of a power supply module. A first sampling terminal of the voltage detection circuit samples the voltage of the AC power network between the AC power network and the disconnecting relay, and an output of the voltage detection circuit is connected to a control terminal of the disconnecting relay. When the AC power network is in the state of overvoltage, the disconnecting relay is disconnected and the power supply module is disconnected from the AC power network. When the voltage of the AC power network is normal, the disconnecting relay is connected. The circuit of the present invention is started up before the busbar voltage reaches its extreme value, and the relay can still work even if only the auxiliary power supply is working among all the components of the power supply module. The auxiliary power supply of the module is still in the work state. The cost of the system is reduced.