The invention relates to a method and a device for detecting the overheat fault of GIS (Gas Insulated Switchgear) internal conductors, which belong to the technical field of fault diagnosis of electric equipment of power systems and can effectively detect the overheat fault of the GIS internal conductors. The device comprises conductors and a GIS shell, wherein two conductors arranged transversely and longitudinally are arranged inside the shell, and the other end of the transverse conductor is sequentially connected with a basin-type insulator A and a connection terminal A; the other end of the longitudinal conductor is sequentially connected with a basin-type insulator B and a connection terminal B; the conductors are internally connected with the basin-type insulator A and the basin-type insulator B and positioned inside the GIS shell to form a whole conductive circuit; an isolating switch and a testing flange are arranged on the shell, and each conductor is connected with a contact seat and a conductive rod. According to the method and the device, the temperature of the GIS internal conductors is obtained by infrared-thermal image detection of the shell, so that the overheat fault of the GIS internal conductors is effectively detected, safe and stable operation of GIS is ensured, and the detection effect and the safety of workers in the live working process are significantly improved.