In　order　to　reveal　the　shear　failure　mechanism　of　CFRP　sheets　strengthened　reinforced　concrete　(RC)　beams,　a　three-dimensional　(3D)　meso-scale　simulation　method　was　adopted,　which　simultaneously　considered　the　meso-heterogeneity　of　concrete　materials,　the　interaction　between　reinforcement　and　concrete,　and　the　interaction　between　CFRP　sheets　and　concrete.　A　3D　meso-scale　numerical　analysis　model　of　CFRP　sheets　strengthened　RC　beams　was　established.　The　influence　of　stirrups,　CFRP　sheets　and　the　interaction　between　them　on　the　shear　failure　behavior　of　RC　beams　were　emphatically　analyzed,　and　a　modified　formula　of　shear　strength　of　CFRP　sheets　strengthened　RC　beams　was　established.　The　results　show　that　the　shear　bearing　capacity　of　beams　increases　with　the　increase　of　stirrup　ratio　and　fiber　ratio,　however　the　increase　range　decreases　with　the　increase　of　stirrup　ratio　and　fiber　ratio.　Both　the　stirrup　strains　and　CFRP　strains　are　closely　related　to　the　position　of　the　main　oblique　crack,　the　closer　to　the　main　oblique　crack,　the　greater　the　strains　are,　and　the　peak　strain　decreases　with　the　increase　of　stirrup　ratio　and　fiber　ratio;　when　the　CFRP　fiber　ratio　increases　from　0.　066　8%　to　0.　267　2%,　the　strain　of　CFRP　decreases　by　45.　9%,　and　when　the　stirrup　ratio　increases　from　0.　2%　to　0.　8%,　the　strain　of　CFRP　decreases　by　30.　6%　.　There　is　an　adverse　interaction　between　stirrups　and　CFRP　sheets,　and　their　contributions　to　the　shear　bearing　capacity　of　the　beam　cannot　be　simply　superimposed.　The　error　between　the　experimental　value　and　the　prediction　of　the　modified　calculation　formula　of　shear　bearing　capacity　of　CFRP　sheets　strengthened　RC　beams　considering　the　influence　of　the　stirrup　ratio,　fiber　ratio　and　their　interaction　is　less　than　20%,　indicating　that　the　formula　is　accurate　and　reasonable,　and　can　be　used　to　predict　and　calculate　the　shear　bearing　capacity　of　RC　beams　strengthened　with　CFRP　sheets.　©　2024　Science　Press.　All　rights　reserved.