The utility model relates to a localization of fault and monitoring devices of transmission line shorted to earth, its laser lamp -house's signal output part connects fiber coupler's first communication end, the one end of an optic fibre among fiber coupler's the second communication end connection composite fiber -optic overhead ground wi, the signal communication end of faraday rotation mirror is connected to the other end of this optic fibre, photoelectric detector's signal input part is connected to fiber coupler's third communication end, photoelectric detector's signal output part connects data collection card's signal input part, data collection card's signal output part connects the signal input part of industrial computer. The utility model discloses sensor and data transmission passageway are only regarded as with the optic fibre among the composite fiber -optic overhead ground wi to no extra sensor on outfield and transmission line, can solve communication problem, mains operated problem that traditional monitoring devices exists under abominable climatic conditions.