Abstract: Li-Mg alloys, as cathode materials for lithium batteries, have broad application prospects in the field of new energy, and the preparation of Li-Mg alloys by molten salt electrolysis has great advantages. The electrochemical behavior of Mg²⁺ on a tungsten electrode in LiCl-KCl-MgCl₂ melt and the Li-Mg co-deposition process were studied by a three-electrode system, respectively. The effect of MgCl₂ concentration on electrolytic co-deposition of Li-Mg was also investigated. The experimental results of square wave voltammetry and timing current method show that the one-step two electrons reduction of Mg²⁺ to metallic Mg on the tungsten electrode is an instantaneous nucleation process, which is not affected by temperature. The results of the timing potentiometric experiment show that with the increasing concentration of MgCl₂, the cathodic current density required for the electrolytic co-deposition of Li-Mg from LiCl-KCl-MgCl₂ melt is gradually increased. When the MgCl₂ concentration in the LiCl-KCl-MgCl₂ melt is 5%, the minimum cathodic current density to achieve Li-Mg co-deposition is 0.287 A/cm². The galvanostatic electrolysis results show that when the MgCl₂ concentration is less than or equal to 5%, the metal Mg content in the Li-Mg product increases with MgCl₂ concentration in the melt. When the MgCl₂ concentration reaches 10%, electrolysis only obtains metal Mg.