Abstract: In order to solve the problem of power supply dead zones of an energy extraction device of a conventional current transformer under a weak current of an overhead wire, this paper proposes an energy extraction method for multistage transformer set ground wires with resonance compensation. Firstly, the principle of the method is analyzed, the equivalent circuit model is established, and the functional relationship between the related parameters and the current and output power of each circuit in the system is deduced. Secondly, reactive power compensation is carried out based on the matching capacitance of system parameters to achieve the maximum power output of the system. Then, a simulation circuit is designed to verify the feasibility of the proposed energy extraction method. Finally, an experimental device is built to verify the feasibility of the scheme. The experimental results show that, when the ground current is as low as 3 A, the output power of the device can reach 1.46 W, which is 9～10 times of the output power of the conventional resonant compensation method of the transformer, and meets the power supply requirements of online monitoring terminal equipment.