Main　group　Bi-based　materials　have　gained　popularity　as　N2　reduction　reaction　(NRR)　photo/electrocatalysts　due　to　their　ability　to　inhibit　competitive　H2　evolution　reactions　(HER)　and　the　unique　N2　adsorption　activities.　The　introduction　of　defects　in　Bi-based　catalysts　represents　a　highly　effective　strategy　for　enhancing　light　absorption,　promoting　efficient　separation　of　photogenerated　carriers,　optimizing　the　activity　of　free　radicals,　regulating　electronic　structure,　and　improving　catalytic　performance.　In　this　review,　we　outline　the　various　applications　of　state　of　the　defect　engineering　in　Bi-based　catalysts　and　elucidate　the　impact　of　vacancies　on　NRR　performance.　In　particular,　the　types　of　defects,　methods　of　defects　tailoring,　advanced　characterization　techniques,　as　well　as　the　Bi-based　catalysts　with　abundant　defects　and　their　corresponding　catalytic　behavior　in　NRR　were　elucidated　in　detail.　Finally,　the　main　challenges　and　opportunities　for　future　development　of　defective　Bi-based　NRR　catalysts　are　discussed,　which　provides　a　comprehensive　theoretical　guidance　for　this　field.　In　this　review,　the　categories,　construction　strategies　and　advanced　characterization　techniques　of　defect　engineering　in　current　Bi-based　NRR　catalysts　are　summarized,　and　the　main　challenges　and　opportunities　for　the　future　development　of　defective　Bi-based　NRR　catalysts　are　discussed,　providing　a　comprehensive　theoretical　guidance　for　this　field.　image