Abstract: At 725℃,MgCl₂-KCl-NaCl-CaCl₂ molten salt was used for the electrolysis of magnesium chloride.Results show that in the course of magnesium electrolysis,cathode overvoltage η_c is not large,only 12~51 mV,the overvoltage of the electrolysis process is mainly caused by the anode;the diffusion-limited current id of the cathodic process is 1.56 A/cm²;the number of electron transfer of the cathodic process is 1.98;while there is a pre-conversion step MgCl⁺=Mg²⁺+C1^-before the reversible electron transfer step.CV was used to study magnesium ions behavior in the molten salt electrolyte with four different ratios of CaCl₂.With changing CaCl₂ from 10 percent to 40 percent,while maintaining MgCl₂ to be 10 percent and the mass ratio of NaCl and KCl to be 6:1,as the amount of CaCl₂ increased,magnesium ions integrate into the complexing anions,which are not easy to move.As a result,the migration current of magnesium ions decreases,the magnesium ions deposition potential gradually moves to the negative direction from-1.595 V to which codeposition of magnesium with Ca and Na takes place,cathodic peak current Ipc gradually increases,the absolute value of the difference between anodic peak potential and cathodic peak potential |φ_pa-φ_pc| gradually increases,and the reversibility of cathode discharge reaction gradually lowers.