Objective To understand the effect of NH₄HF₂ on the cathodic process of iron electrodeposition. Methods Linear sweep voltammetry, single-potential step chronoamperometry and AC impedance spectroscopy were adopted to study the electrocrystallization of iron in plating solutions containing different concentrations of NH₄HF₂ . Results With the increase in the concentration of NH₄HF₂ , the cathodic polarization of iron electrodeposition was decreased; in the Step-potential range of-1. 225 ~-1. 300 V, the electrocrystallization of iron on glassy carbon electrode followed 3D instantaneous nucleation regardless of the concentration of NH₄HF₂ ; when the concentration of NH₄HF₂ increased, the outward growth rate of crystal nucleus and the double layer capacitance were enhanced, however the charge transfer resistance of solution / cathode interface was obviously decreased and the solution resistance was slightly declined. Conclusion The addition of NH₄HF₂ could accelerate the electrodeposition of iron and increase the outward growth rate of crystal.