A system for monitoring a power transmission line of a power grid, including a first comprehensive sensor (402, 502) disposed at the intermediate position of a power transmission line between two towers including an altimeter, a first acceleration sensor, a temperature and humidity sensor and a rainfall sensor; a second comprehensive sensor (404, 504) disposed at the cable connector of the power transmission line including a leakage current sensor, a tension sensor and a wind speed and direction sensor; and a second acceleration sensor (406, 506) disposed at the intermediate position of the power transmission line between the cable connector of the power transmission line and the first comprehensive sensor (402, 502). A method for monitoring a power transmission line of a power grid, including a step of monitoring the sag condition, wind yaw angle, motion and position tracking, flutter conditions, breeze vibration level, fatigue life and icing situation of a power transmission line. The method and system for monitoring a power transmission line of a power grid effectively prevent and reduce incidents of the power transmission line of the power grid based on sensor multi-dimensional sensing technology combined with the advantages of wireless sensor network technology.