Nanocrystalline alloy exhibit superior characteristics that are not typically found in conventional coating and its formation is usually induced by additives. However, the influence mechanism of additives on the electro-deposition process was rare to be investigated, especially in the molecular scale. In this study, nanocrystalline Zn-Ni alloy was electrodeposited from the bath containing 2-aminopyridine as a novel additive and the influence mechanism of 2-aminopyridine in contrast with triethylenetetramine, vanillin and coumarin on electrodeposition of nanocrystalline Zn-Ni alloy was studied by the combined theoretical and experimental studies. It is found that intermediate Zn-ad(+) can catalyze the reduction of Zn2+ and Ni2+. The electrodeposition mechanism of Zn-Ni alloy is unchanged both without and with 2-aminopyridine, however an increased overpotential is observed with 2-aminopyridine, which is related to its strong adsorption on electrode surface. Triethylenetetramine increase the Zn-Ni deposition overpotential by complexing with metal ions. Vanillin and coumarin is achieved mainly by their spot adsorption of oxygen atoms on electrode surface. While synergistic surface adsorption of the amine group and adsorption ring plane in 2-aminopyridine maximizes the Zn-Ni deposition overpotential, leading to the formation of nanocrystalline Zn-Ni alloy.