Abstract: An Fe-Ni alloy coating on 20 steel was prepared by electrodeposition technology. The effects of Fe²⁺ concentration in the bath on the deposition rate, chemical composition, phase structure, micro-hardness and corrosion resistance of the coating were investigated, and the corrosion mechanism was analyzed. Experimental results show that the Fe-Ni alloy coating is nano-crystaIline, and the iron content in the coating increases with increasing Fe²⁺ concentration in the bath. The change in micro-hardness of the Fe-Ni coating is related to the ordered solid solution degree of Fe atoms in the Ni lattice. The corrosion resistance of the Fe-Ni alloy coating is superior to 20 steel, and it is the best when the Fe²⁺ concentration is 0.01 mol· L^-1. With the increase of iron content in the coating, the content of Fe-Ni alloy phase, which has passivation properties and high nickel ratio, and the corrosion resistance decrease. But the nanostructure of Fe-Ni alloy phase is significant refined, and it accelerates the passivity, and thus the corrosion resistance is improved. Due to the contradiction the relationship between corrosion resistance and coating iron content is not obvious. High porosity is one of the reasons for the low corrosion resistance of the Ni-Fe alloy coating.