Piezo-photocatalysis　is　a　frontier　technology　for　converting　mechanical　and　solar　energies　into　crucial　chemical　substances　and　has　emerged　as　a　promising　and　sustainable　strategy　for　N2　fixation.　Here,　for　the　first　time,　defects　and　piezoelectric　field　are　synergized　to　achieve　unprecedented　piezo-photocatalytic　nitrogen　reduction　reaction　(NRR)　activity　and　their　collaborative　catalytic　mechanism　is　unraveled　over　BaTiO3　with　tunable　oxygen　vacancies　(OVs).　The　introduced　OVs　change　the　local　dipole　state　to　strengthen　the　piezoelectric　polarization　of　BaTiO3,　resulting　in　a　more　efficient　separation　of　photogenerated　carrier.　Ti3+　sites　adjacent　to　OVs　promote　N2　chemisorption　and　activation　through　d–π　back-donation　with　the　help　of　the　unpaired　d-orbital　electron.　Furthermore,　a　piezoelectric　polarization　field　could　modulate　the　electronic　structure　of　Ti3+　to　facilitate　the　activation　and　dissociation　of　N2,　thereby　substantially　reducing　the　reaction　barrier　of　the　rate-limiting　step.　Benefitting　from　the　synergistic　reinforcement　mechanism　and　optimized　surface　dynamics　processes,　an　exceptional　piezo-photocatalytic　NH3　evolution　rate　of　106.7 µmol g−1 h−1　is　delivered　by　BaTiO3　with　moderate　OVs,　far　surpassing　that　of　previously　reported　piezocatalysts/piezo-photocatalysts.　New　perspectives　are　provided　here　for　the　rational　design　of　an　efficient　piezo-photocatalytic　system　for　the　NRR.　©　2023　Wiley-VCH　GmbH.