It is difficult to accurately and quickly locate the fault section and outage range after power failure in a distribution network with low-level automation. To solve this problem, a fault location and diagnosis method based on sudden drop ratio (SDR) of the feeder active load is proposed. After the feeder SDR exceeds a certain threshold, the active power of each distribution transformer on the faulty feeder is predicted using the historical load data in the metering automation system, and the load proportion of each switch is calculated. By comparing the feeder SDR and the power proportion of each switch, the fault trip switch and power failure range are judged. Analysis of the results of an engineering example show that the method can accurately locate the fault trip switch, and has good real-time performance. It provides a new fault diagnosis technique for a distribution network independent of the distribution network automation system. This work is supported by the Science and Technology Project of Yunnan Power Grid Co., Ltd. (No. YNKJXM20191129 and No. YNKJXM20191176) and the National Natural Science Foundation of China (No. 51677060).