The popularization of intelligent equipment in the low-voltage distribution network provides a new research direction for real-time diagnosis and initiative rush repair of low-voltage distribution network faults. First, the information source of fault diagnosis and verification method are analyzed. Secondly, tree structure diagram is used to describe the topological structure of the low-voltage courts. And an active fault diagnosis process is proposed. Then, the fuzzy set theory is used when some equipment running state information is missing. Finally, based on PSCAD, the simulation model including the key links such as medium-voltage feeder, low-voltage distribution transformer, low-voltage branch box and end-user is built. The control module is designed according to the research process, and the feasibility and effectiveness of the scheme are verified through simulation results. This work is supported by the Science and Technology Project of State Grid Corporation of China (No. KJ19-1-11).