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/TiO2　catalyst,　identified　through　density　functional　theory　(DFT)　calculations　as　the　synergic　active　site　for　NO3RR.　It　is　found　that　Cu-O-Ti-Ov　site　facilitates　the　adsorption/association　of　NOx-　and　promotes　the　hydrogenation　of　NO3-　to　NH3　via　adsorbed　*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/TiO2　catalyst　with　rich　Cu-O-Ti-Ov　sites　achieves　an　NH3　yield　rate　of　3046.5　mu　g　h-1　mgcat-1　at　-1.0　V　vs.　RHE,　outperforming　most　of　the　reported　activities.　Furthermore,　the　construction　of　Cu-O-Ti-Ov　sites　significantly　mitigates　the　leaching　of　Cu　species,　enhancing　the　stability　of　the　Cu/TiO2　catalyst.　Additionally,　a　mechanistic　study,　using　in　situ　characterizations　and　various　comparative　experiments,　further　confirms　the　strong　synergy　between　Cu,　Ti,　and　Ov　sites,　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.　Published　by　Elsevier　B.V.　All　rights　reserved.