Abstract: In the safety monitoring of transmission towers, traditional electronic sensors are susceptible to electromagnetic interference, wiring complexity, signal can not be transmitted over long distances, etc. To adress these issues, this paper studied a fiber grating sensing technology based on the transmission tower online automatic monitoring system. Fiber grating strain gauge and inclinometer are designed for monitoring the tilt angle and stress deformation of the sensitive position of transmission tower, and fiber grating demodulator is developed for real-time data acquisition, processing and transmission. Instrumentation tests and engineering applications show that the system can realize safe and automatic monitoring of the structural health status of transmission towers, with high accuracy, good stability and fast response speed, which provides a more comprehensive monitoring means to ensure the safe and stable operation of the power grid, and has the value of popularization.