Proposed in this paper is a method of utilizing a capacitive transducer to harvest the electric potential energy stored in the space around the AC transmission line，which helps to supply power to the on-line -monitoring system installed on a transmission tower． First，the circuit model of the potential energy-harvesting system and the relationship between the load resistance and the output power are analyzed，and a way to harvesting the maximum energy is presented． Then，the electric field distribution at the tower head of a 500kV AC double-loop transmission line is simulated，and the places suitable for transducer installation are determined． Finally，an experiment is con-ducted by adopting a capacitive transducer with a radius of 40cm and an interval of 15cm，and about 5mJ of energy is obtained at 50kV in 24s，which means that the capacitive transducer can afford an output power of 208 μW to meet the minimum power limit of wireless sensor nodes． In practically application，there is higher operating voltage compared with the experiment，by utilizing the high-intensity electric field efficiently on the tower with optimized capacitive transducer，enough energy will be harvested to power the on-line -monitoring system．