This study employs first-principles calculations to investigate the pollutions adsorption behavior of the three lowest-energy iron surfaces ((110), (100), and (320)), focusing on the effects of Cl, S, and NH4Cl on surface work function and corrosion mechanisms. Cl adsorption significantly reduces the work function difference between the three surfaces from 0.8293 eV to 0.079 eV, shielding the surface’s electrostatic potential and reducing the tendency for galvanic corrosion but shifts the corrosion mechanism from galvanic corrosion to direct dissolution. In contrast, S adsorption only reduces the work function to 0.6529 eV, still maintaining a high driving force for galvanic corrosion. The presence of NH4+ weakens the interaction between Cl and the surface, but also reduces the shielding effect on the surface work function, causing the galvanic corrosion tendency to reappear. Analysis of surface electrostatic potential distribution shows that when NH4+ and Cl are co-adsorbed, the effect of charge on the vacuum electrostatic potential is partially canceled, resulting in smaller work function changes. Despite this, Cl still forms chemical bonds with the surface, and both corrosion mechanisms may act simultaneously, accelerating the corrosion process. This study provides theoretical insights into corrosion mechanisms in environments with multiple pollutants and offers a reference for predicting material corrosion lifespans.