The invention discloses a coupler which can carry out bus switch; the coupler comprises a switch structure and a coupling structure, wherein the switch structure consists of a switch control port, two transfer relays and a terminal resistor; the input ends of the two transfer relays are connected with the switch control ports; the terminal resistor is connected between normally open contacts; normally closed contacts are connected with the first bus ports; the coupling structure consists of a coupling transformer and an insulation resistor; one end of the coupling transformer is connected with a sub-bus port, while the other end thereof is connected with the insulation resistor; meanwhile, the common terminal connect of the two transfer relays of the switch structure is connected with the otherend of the insulation resistor and then connected with the second bus port. The coupler can reduce the wiring of the bus system and the varieties and quantities of couplers in the system and facilitate the on-line default inspection.