The invention relates to a multi-end transmission line fault distance measurement method based on a WAMS system, belongs to the electric power system field and utilizes normal data and fault data measured by the WAMS system to carry out fault positioning of a main network and branch networks of a power transmission line. The method comprises steps of (1), fault distance calculation based on single-end PMU measurement data; (2), dual-end transmission network main network fault node determination; (3), dual-end branch line fault distance calculation; and (4), fault point position determination.The method is advantaged in that the WAMS system data is fully utilized, not only can accurate main line fault positioning be realized, but also accurate dual-end branch line fault positioning can berealized, the monitoring application scope of the WAMS system is expanded, and relatively high accuracy and reliability are realized.