A method and an apparatus for controlling a shutoff device, and a shutoff device. The shutoff device includes N main switching transistors and N bypass switching transistors. The method includes: controlling the N main switching transistors to be turned on after receiving a heartbeat signal; determining whether a power supply voltage of a processor is less than a first under-voltage protection voltage; and if so, controlling the N main switching transistors to be turned off, and controlling the N bypass switching transistors to be turned on. Thus, N photovoltaic modules and N main switching transistors corresponding to a shutoff device are separated from multiple photovoltaic module groups, so that the photovoltaic module groups corresponding to other shutoff devices can normally output DC voltage to an inverter, and the inverter can normally output AC power for integration into a power grid, thereby ensuring the normal operation of the photovoltaic system.