The invention relates to an early determination method for a substation grounding grid. The method includes the steps: acquiring total fault current and current divider coefficient of the grounding grid and calculating buried short-circuit current; acquiring the size of a station zone of a substation and calculating the total area of the station zone; calculating the minimum section of a grounding body and selecting the shape and the section of the grounding body; calculating and checking the grounding resistance of the grounding body; calculating and checking maximum contact potential and step voltage of the station zone; performing economic and technical comparison on the grounding body meeting requirements to determine the optimal grounding grid design scheme; generating a grounding grid design calculation sheet, an engineering quantity list and an estimation sheet or approximate estimation sheet. The optimal grounding grid design scheme can be early determined, the method effectively solves the problem that a detailed engineering structure and use materials cannot be accurately determined at researchable and preliminary design stages, and an early design method is provided for the substation grounding grid engineering.