The utility model discloses an early warning system for a concealed area of a transformer substation. The early warning system includes a monitoring unit installed in the concealed area and a supervision unit in a monitoring room, the supervision unit and the monitoring unit communicate through a network, the monitoring unit includes a camera, a loudspeaker and a light supplementing lamp, and the supervision unit includes a display and signal input equipment. The early warning system has the advantages that real-time monitoring of the concealed area by staff can be facilitated, labor intensity and task difficulty of an inspection tour in the concealed area by the staff are greatly reduced, the problem that conventional and original inspecting methods of prying a cover plate and drilling a cable duct have hidden danger of inspection dead angles is solved, watch keepers can get rid of frequent and repeated inspection work, manpower is saved, the watch keepers have vigor to put in more safety management tasks that need people to carry out, and through detection and alarm issuing of foreign matter intrusion of the concealed area, related personnel are prompted to carry out targeted inspection, thereby improving work efficiency.