Abstract: In order to ensure the normal use of medium voltage distribution lines, give full play to their own functions, make scientific prevention and control and handle line fault tripping. Starting from analyzing the influencing factors of line fault tripping, including flashover and discharge of insulator string, low protection setting value and switching on impact. Discuss prevention suggestions and treatment schemes. Reduce tower grounding resistance, prevent and control external force invasion, update insulators, install amp clamps, and control closing impulse current. Hope to bring some help to the practice of peers from the theoretical level.