Bismuthoxyselenide　(Bi2O2Se)　is　a　two-dimensional(2D)　layered　semiconductor　material　with　high　electron　Hall　mobilityand　excellent　environmental　stability　as　well　as　strong　spin-orbitinteraction　(SOI),　which　has　attracted　intense　attention　for　applicationin　spintronic　and　spin　optoelectronic　devices.　However,　a　comprehensivestudy　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,　wefind　that　the　HDPC　originates　from　surface　states　with　C　(　s　)　symmetry　in　Bi2O2Se,　which　can　be　attributed　to　the　circular　photogalvanic　effect(CPGE)　and　circular　photon　drag　effect　(CPDE).　It　is　revealed　thatthe　HDPC　current　almost　changes　linearly　with　the　source-drainvoltage.　Furthermore,　we　demonstrate　effective　tuning　of　HDPC　inBi(2)O(2)Se　by　ionic　liquid　gating,　indicating　thatthe　spin　splitting　of　the　surface　electronic　structure　is　effectivelytuned.　By　analyzing　the　gate　voltage　dependence　of　HDPC,　we　can　unambiguouslyidentify　the　surface　polarity　and　the　surface　electronic　structureof　Bi2O2Se.　The　large　HDPC　in　Bi2O2Se　nanosheets　and　its　efficient　electrical　tuning　demonstratethat　2D　Bi2O2Se　nanosheets　may　provide　a　goodplatform　for　opto-spintronics　devices.