The reliability and efficiency of the grounding system in substations is of utmost importance for the safety of the electrical grid. In China, the grounding grids of substations are primarily composed of galvanized steel, carbon steel, and copper, all of which are susceptible to corrosion from soil during operation. This study thoroughly examines the effects of typical Cl− ions and soil water content on the corrosion behavior of a Q235 steel in situ. The data suggest that there is a negative correlation between soil moisture and grounding grid corrosion, whereas dissolved salts, particularly Cl− ions in soil, correlate positively.