With the commissioning of UHVDC transmission lines in China, more and more attention has been paid to ground potential distortion and electromagnetic interference caused by direct current into the ground.Due to differences of soil structure in different regions, the distribution of surface potential is not the same.In order to study the law of surface potential distribution during unipolar operation of the Yanmenguan converter station, a three-layer soil resistivity model of Yanmenguan according to the field measurement using Wenner four-electrode method is established.Then the potential of substations, wind farms, and gas pipelines within 100 km of the grounding electrode at rated current is calculated.Simultaneously, the expression of the change of ground potential with distance is determined.Finally, the effects of injected current, soil resistivity, local resistivity and buried metal pipelines on the distribution of ground potential are studied.The simulation results show when the grounding electrode is a double ring structure, the ground potential decreases with distance.The injection current and soil resistivity have a greater influence on the surface potential distribution, and the buried metal pipes and local uneven resistivity have little effect on the surface potential.