Revealing　the　synergistic　catalytic　mechanism　involving　multiple　active　centers　is　crucial　for　understanding　multiphase　catalysis.　However,　the　complex　structures　of　catalysts　and　interfacial　environments　pose　a　challenge　in　thoroughly　exploring　the　experimental　evidence.　This　study　reports　the　utilization　of　a　CuNi　dual-atom　catalyst　(Cu/Ni-NC)　for　the　electrochemical　reduction　of　CO2.　It　demonstrates　a　high　Faradaic　efficiency　of　CO　exceeding　99%,　remarkable　reaction　activity　with　a　partial　current　density　surpassing　-300　mA　cm(-2),　and　prolonged　stability　for　more　than　5　days　at　a　current　density　of　-200　mAcm(-2).　Operando　characterization　techniques　and　density　functional　theory　calculations　reveal　that　Ni　atoms　function　as　active　sites　for　the　activation　and　hydrogenation　of　CO2,　while　Cu　atoms　serve　as　active　sites　for　the　dissociation　of　H2O,　supplying　protons　for　the　subsequent　hydrogenation　process.　Moreover,　the　electronic　interactions　between　Ni　and　Cu　atoms　facilitate　the　formation　of　*COOH　and　the　dissociation　of　H2O,　illustrating　a　synergistic　reduction　of　CO2　at　the　dual-atom　sites.