<p>This work explores the effects of Fe and Mn elements on anti-corrosion property of CoCrNi MEA in a carbonate/bicarbonate solution. The corresponding analyses imply that the corrosion resistance of the MEA is remarkably better than that of CoCrFeMnNi high-entropy alloy by comparing their passive current densities (i_p), corrosion rates, and corrosive morphologies. Three main factors lead to the difference in their corrosion resistance, namely microstructure, chemical composition, and passivation film. For the MEA, larger grain size, fewer amounts of oxides, and more protective passive film with lower carrier density improve its corrosion resistance. The Fe and Mn additions result in the generation of iron and manganese compounds, which enhance the electrochemical reaction and decrease the protection of surface film, presenting a lower protective capacity. Furthermore, due to the existence of more oxides, serious micro-galvanic corrosion between oxides and HEA substrate is generated, which greatly promotes the pitting occurrence of the HEA.</p>