Abstract: With the decreasing area of urban substation and the increasing short-circuit current,it is more and more difficult to achieve the safety index of grounding grid such as contact potential and grounding resistance.Taking the 220 kV general design scheme A3-2 of State Grid Corporation of China as an example,the traditional design was optimized.Firstly,the optimal compression ratio and mesh size of horizontal ground grids with unequal spacing were studied based on the simulation analysis of CDEGS software.Then,the impact of short vertical direct grounding electrode on grounding resistance was evaluated from the physical model of grounding grid.Finally,the grounding effect of long vertical direct grounding electrodes of different amount and length were simulated and analyzed.Combined with the specification,the voltage withstand level of primary and secondary equipment and the cable grounding mode were evaluated,which reasonably reduces the requirements of the specification for grounding resistance.The results show that the unequal spacing horizontal grounding grid with four 40 m vertical grounding electrodes is much better than the traditional design in reducing the contact potential and grounding resistance,and meets the safety indexes of the grounding grid.