Abstract: In this paper, the online energy extraction methods of overhead transmission lines are discussed. According to the different energy extraction principles, the online energy extraction methods are divided into two ways: using natural energy to extract energy and using transmission lines to extract electric energy. The paper elaborates, and compares the three main methods of electrostatic field energy extraction, magnetic field energy extraction and eddy electric field energy extraction involved in the extraction of electrical energy from transmission lines, from the aspects of feasibility and impact on transmission line insulation, lightning protection, etc. analyze.