Abstract: In view of problems of limited terrain, short effective dispersion length, and low resistance reduction efficiency in the extensional resistance reduction of the grounding grid of incoming line section of mine substation, a resistance reduction method using long -distance extension lead for auxiliary grounding of incoming line tower was proposed. The grounding calculation software CDEGS is used to establish simulation model of "Τ" type, "Γ" type, box type, vertical type unidirectional auxiliary grounding network, and study stray current characteristics of unidirectional auxiliary grounding grid of steel tube tower and corresponding influencing factors. The research results show that the longer the extension lead, the higher the resistance reduction efficiency; when the extension lead length exceeds 60 m, the resistance reduction efficiency is stable at about 80% under the action of high -frequency current; the "Γ" type unidirectional auxiliary grounding grid has stable stray current characteristics, strong shunting ability, and its resistance reduction effect is the best; resistance reduction efficiency of the unidirectional auxiliary grounding grid is more than 70% under different soil conditions. In practical engineering applications, it is recommended to determine the extension lead length and terminal structure of the auxiliary grounding grid according to the actual soil conditions, and to lay the auxiliary grounding grid to areas with low soil resistivity or to take local soil replacement measures for areas with high soil resistivity to improve the resistance reduction efficiency of unidirectional auxiliary grounding grid of the incoming line tower.