A method and an apparatus for controlling a shutoff device, and a shutoff device. The method is applied to a processor of the shutoff device. The method includes: determining whether a heartbeat signal is received continuously during a first preset period; if so, controlling the N main switching transistors to be turned on, and determining whether the heartbeat signal is not received continuously during a second preset period; and if so, controlling the N main switching transistors to be turned off, and controlling the release circuit to be turned on to release a voltage on the bus. A release circuit is controlled to release voltage on the bus to the ground, thereby rapidly reducing the voltage on the bus, avoiding person danger and safety accidents caused by the long-term presence of the direct current high voltage on the bus, and improving the safety and reliability of a photovoltaic system.