The invention discloses an overhead line discharge drainage on-line monitoring and precision positioning device which comprises an information analysis platform, a wireless hub and a number of monitoring terminals. Each monitoring terminal has a unique ID. The invention further discloses an overhead line discharge drainage on-line monitoring and precision positioning method. A number of monitoring terminals in the device form a wireless ad hoc network. Monitoring data are sent to the wireless hub and then sent to the information analysis platform. The information analysis platform calculates and analyzes the data, determines whether a fault occurs and the fault type in combination with the internally stored data model, and carries out positioning in combination with ID information in the data. According to the invention, the grounding resistance and the drainage event of an overhead line can be monitored in real time; a failed tower can be accurately located; an abnormal event which does not cause tripping can be analyzed, which facilitates timely maintenance of a failed line and a line with hidden danger. The device and method are used for on-line monitoring and precise positioning of overhead line drainage.