A mathematical model for estimating the electric potential at the ground surface of an earthing system of wind turbines using ring electrode is presented. This model depends on the induced charge resulting from the injected current in the ring electrode that is buried in the earthing layers and connecting with turbine body. A three dimension numerical model to analyse wind turbine earthing systems is proposed. The proposed technique depends on the determination of the electric field intensity and the distribution of the injected current into the surrounding soil around an earthing system of wind turbine. The finite element method is used for this purpose. The proposed technique is applicable to simple and complex earthing systems with uniform soil.