Abstract: With the challenge of energy and environmental crisis, green metallurgy technology has become the focus of attention in the industry. The pyrometallurgical process of copper smelting using copper sulfide ore as raw material produces a large amount of harmful gas SO₂, which requires additional energy for conversion. In contrast, the direct electrolysis of copper sulfide into metallic copper and elemental sulfur by molten salt electrolysis is environmentally friendly. In the present work, the cathodic electrochemical process of copper electrodeposition in NaCl-KCl-MgCl₂-Cu₂S melt at 700 ℃ was investigated. The results showed that Cu⁺ was reduced to Cu through a one-step electron transfer with a diffusion coefficient of 1.23×10^-5 cm²/s; the nucleation growth of Cu electrodeposition was a diffusion-controlled three-dimensional instantaneous nucleation mechanism, and the nucleation grew into an irregular particle microstructure with a size of tens of nanometers to several micrometers.