Abstract: An approach to calculate parameters of grounding power grid is introduced by using of Green function, through which self resistance and mutual resistance can be calculated by image method, and potential distribution of any irregular grounding power grids after constant current inputting can also be computed in uniform soil conditions. In addition, a software for calculating the potential distribution of grounding system has been developed and used in a 10?10 uniform grounding power grid caculation. The results show that the potential distribution of grounding power grid is higher in middle, its value decreases gradually, and the potential on metal conductors is higher than that on the grid center. The calculation results of a substation grounding power grid verify above conclusion. It also shows that the step voltage changes greatly in transitional edge region from regular grid to irregular grid, and if there exists vertical grounding nodes, the step voltage will become higher. In the end, the software is applied to circle grounding power grid, in which the circle is taken as a regular 16 polygon, and the calculated results are close to the potential distribution of circle grounding systems.