Developing efficient multimetallic electrocatalysts is a key challenge for the industrialization of CO₂ electrochemical reduction (CO₂RR). In this paper, a Cu-Sc bimetallic catalyst system prepared by molten salt electrolysis combined with anodic oxidation treatment was reported, and the impact of Sc content on CO₂RR selectivity was extensively investigated. Controlling the Cu/Sc mass ratio (95:5 to 85:15) resulted in the synergistic optimization of the electronic structure and geometrical configuration of the catalyst surface. The experimental results showed that the CuSc₅ catalyst exhibited excellent CH₄ selectivity (Faraday efficiency of 70.84%) and long-term stability (40 h) at -1.2 V vs. Ag/AgCl. In situ Raman spectroscopy and density-functional theory calculations show that Sc doping induces an upward shift of the d-band center (~0.08 eV) , which reduces the adsorption energy barriers of CO* intermediates. The anodic oxidation procedure creats surface O vacancies that interact with the Sc vacancies, optimizing the conversion pathway of CO2→CHO*→CH₄. The energy barrier of the decisive velocity step (CO*→ CHO*) is the lowest (0.36 eV) with a Cu-Sc atomic ratio 15:1, which is consistent with the experimental observations. This study introduces a new theoretical framework and practical approach for designing extremely efficient rare-earth doped CO₂RR catalysts.