There are a lot of redundancy and incompleteness in the alarm information of distribution network after fault, so it is important to extract the key fault information and get accurate diagnosis results through fault diagnosis in time for assisting the supervisor in dispatching work. Compared with the telemetry information only based on supervisory control and data acquisition (SCADA) system, wide area measurement system (WAMS) provides a unified time scale benchmark for fault alarm timing information by using the whole network synchronous clock, which brings new opportunities for fault diagnosis of distribution network. In this context, based on the sequence of event (SOE) information of synchronous time series, a fault diagnosis method for distribution network based on synchronized time series information characteristics of relay protection is proposed in this paper. Firstly, the stage timing coordination relationship in the relay protection system of distribution network is analyzed, and the time sequence relationship model of synchronous SOE information is established. Then, according to the characteristics of distribution network lines, the decision table method in rough set is improved, and the fault diagnosis rules with better generalization ability and practicability are obtained. Finally, the simulations of electromagnetic transient and diagnostic method are carried out on PSCAD platform, and the accuracy and validity of the diagnostic method are verified by the numerical results.