The electrochemical behavior of impurity elements in lithium electrolysis was studied by cyclic voltammetry.In the process of electrolysis, the deposition of impurity element Mg was prior to Li at the cathode, followed by the underpotential deposition of lithium metal to form magnesium-lithium alloy, and finally the deposition of lithium metal.The reduction electrode process of Mg ²⁺ was controlled by diffusion with diffusion coefficient of 1.44×10 ^-5 cm ²/s.Calcium-lithium co-deposition can occur with a small amount of Ca ²⁺.In the molten salt system with a small amount of NaCl, the impurity element Na was reduced by Li and formed into alloy.With the increase of NaCl content in the electrolyte system, the sodium content in lithium metal increased greatly.The impurity element Fe was preferentially formed at the cathode than Li which was reduced to spongeiron at the cathode to passivate the cathode, resulting in a sharp decrease in the precipitation current of lithium in molten salt system.The reduction electrode process of Fe ³⁺ was controlled by diffusion with diffusion coefficient of 3.14×10 ^-5 cm ²/s.