Ground grid design of substation is very important. It will help prevent the danger caused by the fault which causes the high step voltage and high touch voltage and may cause the operator to die. It also helps prevent damage to equipment and increases reliability for power systems as well. Currently the Gas Insulated Substation (GIS) has been built a lot especially in areas with limited space because it takes less space than the Air Insulated Substation (AIS). In order to create a substation of the GIS model instead of the AIS model. In order to create the GIS instead of AIS including the improvement or maintenance of the substation it is necessary to build another small substation to supply electricity to replace electricity from the original substation. However there are two substation stations in the same area may cause an increase of high-slope ground potential between the ground grid systems of both substations. It will cause high step voltage and high touch voltage while the fault is diminished. Therefore before improvement or maintenance of substation the ground grid distance and the size of the newly constructed substation must be analyzed that what effect on step voltage and touch voltage generation. Including studying the effects of step voltage and touch voltage that will occur.