Abstract: The grounding grid of hydropower stations is critical infrastructure ensuring the safe and stable operation of power systems, with its health status directly impacting equipment and personnel safety.Traditional uniform maintenance strategies struggle to accurately assess the actual condition and risk distribution of the grounding grid, hindering the implementation of differentiated, precision maintenance.To address this, this paper proposed a method for quantifying regional importance of the grounding grid based on corrosion simulation and a dual-indicator evaluation model.First, using the electromagnetic field simulation software CDEGS, the paper systematically simulated the variation patterns of grounding resistance under self-corrosion(localized corrosion only) and heterogeneous corrosion (corrosion in other areas) two typical degradation scenarios.Subsequently, we proposed the Self-Criticality Index, which could characterize the functional attributes of a region, and the Global Support Index, which could reflect its supporting role within the system.Finally, by weighting and integrating these two normalized indices, a comprehensive importance ranking for each zone was obtained.Simulation analysis using a large hydropower station grounding grid as a case study demonstrated that this method can effectively identify critical zones with decisive influence on the electrical performance of the grounding grid.The results can provide a theoretical basis for grounding grid condition assessment and precision maintenance, offering significant engineering application value.