In view of the land area, terrain and other restrictions for the construction of Hunan 220 kV indoors substation and problems of the conventional way of grounding grid design difficult to meet the requirement of operation safety and economic construction in the national standard, proposed the three-dimensional grounding grid technology. First calculates the soil resistivity and the current into the ground, then selects the ground material, and allocates and calculates compound grounding grid with the horizontal grid and vertical grid. Finally checks the touch voltage and step voltage of the three-dimensional ground grid. Data analysis results show that the three-dimensional grounding grid meets the request. It has great reference value for the design of similar grounding system.