The invention discloses a power grid equipment topology-based voltage sag source positioning system, and aims to solve the technical problems of accurate positioning of a voltage sag source, reason classification and the like. On the basis of power grid equipment and voltage sat record, voltage sag event combination and voltage sag event power grid equipment spreading modeling are respectively performed on voltage sag source identification, a power grid equipment topological mode and a voltage sag source identification flow are designed on the basis of the model, system-side voltage sag reasonclassification modeling is performed according to power grid fault data and power grid lightning data, a system-side voltage sag reason classification flow under an instantaneous fault and a permanent fault is proposed, and a large-user voltage sag reason classification flow is proposed according to a user-side load constituent and a load rule. By the power grid equipment topology-based voltage sag source positioning system, the problems of accurate positioning of the voltage sag source, system-side voltage sag reason classification and user-side voltage sag reason classification are solved.