Taking energy from the ground wire is a way of supplying energy for all kinds of sensing and monitoring equipment in the power system transmission network. In this paper, firstly, the principle of taking electricity of a typical overhead ground wire was examined. Next, its equivalent parameter model was established. Finally, the equivalent voltage and equivalent impedance of the electricity taking port were mathematically derives. Simulation of a 220 kV line with ATP-EMTP software was carried out. The influence of the energy load on the distribution of ground wire current and the influence of factors including wire current, ground resistance, span range, energy load on the electricity parameters were analyzed. The results show that limited by the induced potential and ground wire self-impedance, the ground wire current did not exceed 10 A. The voltage showed an increasing trend with the increase of impedance, and finally stabilized at about 27 V. When the energy extraction load was 2.5 Ω, the maximum energy extraction power obtained was 175.03 W. These results provide a data basis for the design of subsequent energy takers.