The effect of hydrogen inhibitor on partial current densities of Zn, Fe and differential capacitance of electrode/electrolyte interface, and adsorbing type of hydrogen inhibitor were studied by the methods of electrochemistry. The mechanism of current efficiency improvement were explained from the point of valence electron theory. The results indicate that the partial current density of Fe increases in addition of hydrogen inhibitor, which reaches the maximum of 0.14 A/dm2 when current density is 0.2 A/dm2.Differential capacitance of electrode/electrolyte interface decreases obviously from 20.3 μF/cm2 to 7 μF/cm2 rapidly with the concentration varying from 0 to 20 mL/L, because hydrogen inhibitor chemically adsorbs on active points of Fe electrode surface selectively. Element S in hydrogen inhibitor with negative electricity and strong capacity of offering electron shares isolated electrons with Fe. The adsorption of H atom is inhibited when adsorbing onactive points of Fe electrode surface firstly, and then current efficiency of Zn-Fe alloy electroplating is improved accordingly.