Bismuth　oxyselenide　(Bi2O2Se)　is　a　two-dimensional　(2D)　layered　semiconductor　material　with　high　electron　Hall　mobility　and　excellent　environmental　stability　as　well　as　strong　spin-orbit　interaction　(SOI),　which　has　attracted　intense　attention　for　application　in　spintronic　and　spin　optoelectronic　devices.　However,　a　comprehensive　study　of　spin　photocurrent　and　its　microscopic　origin　in　Bi2O2Se　is　still　missing.　Here,　the　helicity-dependent　photocurrent　(HDPC)　was　investigated　in　Bi2O2Se　nanosheets.　By　analyzing　the　dependence　of　HDPC　on　the　angle　of　incidence,　we　find　that　the　HDPC　originates　from　surface　states　with　Cs　symmetry　in　Bi2O2Se,　which　can　be　attributed　to　the　circular　photogalvanic　effect　(CPGE)　and　circular　photon　drag　effect　(CPDE).　It　is　revealed　that　the　HDPC　current　almost　changes　linearly　with　the　source-drain　voltage.　Furthermore,　we　demonstrate　effective　tuning　of　HDPC　in　Bi2O2Se　by　ionic　liquid　gating,　indicating　that　the　spin　splitting　of　the　surface　electronic　structure　is　effectively　tuned.　By　analyzing　the　gate　voltage　dependence　of　HDPC,　we　can　unambiguously　identify　the　surface　polarity　and　the　surface　electronic　structure　of　Bi2O2Se.　The　large　HDPC　in　Bi2O2Se　nanosheets　and　its　efficient　electrical　tuning　demonstrate　that　2D　Bi2O2Se　nanosheets　may　provide　a　good　platform　for　opto-spintronics　devices.　©　2023　American　Chemical　Society.