Abstract: The imprecise earth resistivity model is the main reason for the inaccurate impact assessment of the conductors on ground or underground and AC networks around DC ground electrode.Earth surface potential（ESP） produced by ground current has the characteristic of concentric circle distribution with the center of the ground electrode.Based on the engineering data of ground electrode and the historical magnetotelluric sounding data of the crust and upper mantle,a three-dimensional earth resistivity model was proposed to evaluate the distribution of ESP around DC ground electrode.It was proved that DC biasing current（DCBC） calculated by three-dimensional earth resistivity model is accurate and reliable by comparing measured data of DCBC in AC networks around Hami DC ground electrode of ±800 kV Tian-Zhong UHVDC project with the modeling result.The model has great significance to the site selection and design of ground electrode and the optimization of DCBC control scheme.