For a long time, Distribution transformer service area lacks effective equipment condition monitoring and operation monitoring methods, and cannot timely grasp information such as power failures in the station area and low-voltage distribution network and positions of power-off, resulting in fault finding and positioning of low-voltage distribution network or user mainly relying on users reported repairs or complaints to 95598, which seriously restrict-ed the efficiency of power supply recovery and customer service. Based on monitored and analyzed in real time of the Transformer Terminal Unit(TTU) to the local information of the distribution transformer station, the low voltage branch box, the meter box and the user intelligent meter, the distributed edge calculation function of TTU is adopted to propose an active fault diagnosis method of low voltage based on TTU, actively grasping the user power outage events and conducting fault research and diagnosis local, solving the problems caused by traditional method such as passive perception of fault, timeliness and information congestion fault for concentrated information collection and diagnosis. Realizing timely and proactively locate faulty areas, and to carry out fault repairs of low voltage distribution network, reduce user blackout time, and improve "active" service and quality service level.