The invention discloses a method and system for pre-warning a power distribution network fault. The system comprises a monitor server, a communication network, and a monitor terminal; and the monitor terminal comprises a network voltage detection circuit, a network current detection circuit, a video acquisition device, a positioning device, a meteorological data acquisition device and a monitor terminal processer. The monitor terminal is used for acquiring data of distribution lines, transformers, switch breakers, isolating switches, capacitors and reactors and obtaining a node-branch association list, a bus node association list, nodes and a branch association matrix; reading the status of the distribution line switch and branch status information; calculating active load power and reactive load power of each node, and updating the obtained information to a master monitor station through a communication network; the monitor server is used for receiving data information sent by a remote monitor terminal through the communication network, displaying and saving the data information of the distribution network in real time, and sending a fault alarm when the distribution network data information exceeds a preset threshold value and isolating fault sections.