<p>The combined impact of alternating current (AC) density and ammonium ion content on the anti-corrosion property of CoCrFeMnNi HEA in a 3.5 wt.% NaCl solution was researched via electrochemical test, atomic force microscope (AFM), and scanning electron microscopy (SEM). Elevated corrosion rate and metastable pitting density confirm that the corrosion resistance of the HEA is gradually declined with rising NH₄⁺ concentration. Increasing AC density induces a transition of the alloy surface status from passivated to active, signifying that a violent anodic dissolution reaction occurs. When AC interference is exerted, the passivation film on the HEA becomes noticeably non-compact, inhomogeneous, and thin, accompanied by a rise in flaw amount. Moreover, the synergistic impact between i_AC and ammonium ion leads to the production of larger and denser corrosion pits on the matrix. The augmented adsorption of aggressive ions and increased H⁺ observably reduce the barrier capability of the protective passivation film, thereby intensifying the corrosion of the alloy, as testified by the rapid rise of corrosion current density.</p>