<p>The corrosion behavior of FeCoNi medium-entropy alloy (MEA) in NaCl solutions with varying concentrations under direct current (DC) interference of different intensities was systematically studied. The results demonstrate that an increase in chloride ion content impairs the corrosion resistance of the MEA, and this adverse effect is further exacerbated after the application of DC density. With the augmented Cl⁻ concentration, the passive region narrows, pitting susceptibility is enhanced, and a higher density of structural defects is produced in the passivation film, which leads to an elevated corrosion rate. Under the combined action of DC and Cl⁻, the passive film suffers severe destruction, and the anti-corrosion performance degrades significantly, which is mainly verified by the emergence of active corrosion features and large-area corrosion pits. The substantial H⁺ generated by DC application and ion adsorption induced by its electric field force cause extensive damage to the passive film and increase Cl⁻ penetration pathways, thus resulting in serious dissolution of the MEA.</p>