The invention relates to overhead distribution networks, in particular to an on-line monitoring system for positioning a failure of a network distribution overhead line. The on-line monitoring system for positioning the failure of the network distribution overhead line solves the problem that a device used for on-line monitoring of the operating state of the overhead distribution network is unavailable at present. The on-line monitoring system for positioning the failure of the network distribution overhead line comprises a distribution remote terminal and a system master station, wherein the distribution remote terminal comprises an overhead line failure detection terminal, a ground signal collector, an overhead handheld remote control, a communication host computer, a first solar cell panel and a second solar cell panel, the system master station comprises a router, a communication interchanger, a data server, a client side and a monitoring center server, the signal transmission end of the overhead line failure detection terminal is connected with the signal transmission end of the communication host computer in a bidirectional mode, and the signal output end of the ground signal collector is wirelessly connected with the signal input end of the router. The on-line monitoring system for positioning the failure of the network distribution overhead line is applicable to the overhead distribution networks.