The electrochemical CO₂ reduction reaction (CO₂RR) holds significant promise in advancing carbon neutrality. Developing catalysts for the electrochemical CO₂RR to multi-carbon (C₂₊) products (e.g., C₂H₄) under industrial-level current density is urgently needed and pivotal. Herein, we report the Cu₂O nanoparticles doped with interstitial carbon atoms (denoted as C-Cu₂O NPs) for the conversion of CO₂ to C₂₊ products. The interstitial carbon promotes the C-Cu₂O NPs to possess abundant unsaturated Cu–O bonds, leading to a high-density Cu^δ+ (0 < δ <1) species. The obtained C-Cu₂O NPs exhibited significant Faradic efficiency (FE) of C₂₊ products approaching 76.9% and a partial current density reaching 615.2 mA·cm^–2 under an industrial-level current density of 800 mA·cm^–2. Furthermore, the efficient electrosynthesis of C₂H₄ achieved an FE of 57.4% with a partial current density of 459.2 mA·cm^–2. In situ electrochemical attenuated total reflection Fourier transform infrared spectroscopy and in situ Raman spectroscopy analyses revealed that C-Cu₂O NPs stabilized the intermediate *CO and facilitated C–C coupling, leading to increased selectivity towards C₂₊ products.