CO2　electroreduction　has　been　regarded　as　an　appealing　strategy　for　renewable　energy　storage.　Recently,　bismuth　(Bi)　electrocatalysts　have　attracted　much　attention　due　to　their　excellent　formate　selectivity.　However,　many　reported　Bi　electrocatalysts　suffer　from　low　current　densities,　which　are　insufficient　for　industrial　applications.　To　reach　the　goal　of　high　current　CO2　reduction　to　formate,　we　fabricate　Bi　nanosheets　(NS)　with　high　activity　through　edge/terrace　control　and　defect　engineering　strategy.　Bi　NS　with　preferential　exposure　sites　are　obtained　by　topotactic　transformation,　and　the　processes　are　clearly　monitored　by　in-situ　Raman　and　ex-situ　X-ray　diffraction　(XRD).　Bi　NS-1　with　a　high　fraction　of　edge　sites　and　defect　sites　exhibits　excellent　performance,　and　the　current　density　is　up　to　ca.　870　mA.cm(-2)　in　the　flow　cell,　far　above　the　industrially　applicable　level　(100　mA.cm(-2)),　with　a　formate　Faradaic　efficiency　greater　than　90%.　In-situ　Fourier　transform　infrared　(FT-IR)　spectra　detect　(OCHO)-O-star,　and　theoretical　calculations　reveal　that　the　formation　energy　of　*OCHO　on　edges　is　lower　than　that　on　terraces,　while　the　defects　on　edges　further　reduce　the　free　energy　changes　(Delta　G).　The　differential　charge　density　spatial　distributions　reveal　that　the　presence　of　defects　on　edges　causes　charge　enrichment　around　the　C-H　bond,　benefiting　the　stabilization　of　the　*OCHO　intermediate,　thus　remarkably　lowering　the　Delta　G.