Electrocatalytic nitrate reduction reaction (NO3RR) has been capturing immense interest in the industrial application of ammonia synthesis, and it involves complex reaction routes accompanied by multi-electron transfer, thus causing a challenge to achieve high efficiency for catalysts. Herein, we customized the Cu-O-Ti-Ov(oxygen vacancy) structure on the Cu/TiO2catalyst, identified through density functional theory (DFT) calculations as the synergic active site for NO3RR. It is found that Cu-O-Ti-Ovsite facilitates the adsorption/association of NOx–and promotes the hydrogenation of NO3–to NH3viaadsorbed *H species. This effectively suppresses the competing hydrogen evolution reaction (HER) and exhibits a lower reaction energy barrier for NO3RR, with the reaction pathways: NO3* → NO2* → HONO* → NO* → *NOH → *N → *NH → *NH2→ *NH3→ NH3. The optimized Cu/TiO2catalyst with rich Cu-O-Ti-Ovsites achieves an NH3yield rate of 3046.5 μg h–1mgcat–1at –1.0 V vs.RHE, outperforming most of the reported activities. Furthermore, the construction of Cu-O-Ti-Ovsites significantly mitigates the leaching of Cu species, enhancing the stability of the Cu/TiO2catalyst. Additionally, a mechanistic study, using in situcharacterizations and various comparative experiments, further confirms the strong synergy between Cu, Ti, and Ovsites, which is consistent with previous DFT calculations. This study provides a new strategy for designing efficient and stable electrocatalysts in the field of ammonia synthesis.