A slave monitor, comprising a first wiring terminal group, a second wiring terminal group, a grounding terminal, a first power supply terminal, and a second power supply terminal, wherein the first wiring terminal group comprises a first wiring terminal and a second wiring terminal, the first wiring terminal is configured to connect to a conducting wire of a cable, and the second wiring terminal is configured to connect to a first primary wiring terminal of an isolation transformer; the second wiring terminal group comprises a third wiring terminal and a fourth wiring terminal, the third wiring terminal is configured to connect to the conducting wire of the cable, and the fourth wiring terminal is configured to connect to a second primary wiring terminal of the isolation transformer; the grounding terminal is configured to connect to a grounding medium of the cable; and the first power supply terminal is configured to connect to a secondary output terminal of the isolation transformer, and the second power supply terminal is configured to connect to a light fixture; wherein the slave monitor is configured for: receiving a first power line carrier signal from a master monitor by using the cable, wherein the slave monitor is directly connected to the cable; and obtaining a control signal from the first power line carrier signal through demodulation; and controlling on/off of the light fixture based on the control signal, wherein the light fixture is connected to the slave monitor, wherein the controlling on/off of the light fixture based on the control signal specifically comprises: setting up or breaking, by the slave monitor based on the control signal, a connection between the secondary output terminal of the isolation transformer and the light fixture, to control on/off of the light fixture. the first wiring terminal group comprises a first wiring terminal and a second wiring terminal, the first wiring terminal is configured to connect to a conducting wire of a cable, and the second wiring terminal is configured to connect to a first primary wiring terminal of an isolation transformer; the second wiring terminal group comprises a third wiring terminal and a fourth wiring terminal, the third wiring terminal is configured to connect to the conducting wire of the cable, and the fourth wiring terminal is configured to connect to a second primary wiring terminal of the isolation transformer; the grounding terminal is configured to connect to a grounding medium of the cable; and the first power supply terminal is configured to connect to a secondary output terminal of the isolation transformer, and the second power supply terminal is configured to connect to a light fixture; wherein the slave monitor is configured for: receiving a first power line carrier signal from a master monitor by using the cable, wherein the slave monitor is directly connected to the cable; and obtaining a control signal from the first power line carrier signal through demodulation; and receiving a first power line carrier signal from a master monitor by using the cable, wherein the slave monitor is directly connected to the cable; and obtaining a control signal from the first power line carrier signal through demodulation; and controlling on/off of the light fixture based on the control signal, wherein the light fixture is connected to the slave monitor, wherein the controlling on/off of the light fixture based on the control signal specifically comprises: setting up or breaking, by the slave monitor based on the control signal, a connection between the secondary output terminal of the isolation transformer and the light fixture, to control on/off of the light fixture.