Taking　reinforced　concrete　cantilever　beams　strengthened　by　CFRP　side　bonding　as　the　research　object,　and　considering　the　meso-heterogeneity　of　the　concrete　and　the　interaction　between　the　CFRP　and　concrete,　a　three-dimensional　meso-scale　numerical　analysis　model　of　CFRP　side　bonding　strengthened　reinforced　concrete　cantilever　beams　without　web　reinforcement　under　monotonic　loading　was　established.　In　this　study,　the　size　of　the　CFRP　fiber　ratio　was　realized　by　changing　the　thickness　of　the　CFRP　strip,　and　the　CFRP　fiber　ratio　was　considered　as　the　dominant　parameter.　Moreover,　based　on　the　previous　experimental　work,　the　influence　of　the　size　and　fiber　ratio　on　the　shear　failure　mechanism　and　failure　mode　of　RC　cantilever　beams　strengthened　with　CFRP　was　studied,　and　the　shear　failure　size　effect　of　RC　cantilever　beams　strengthened　with　CFRP　was　studied.　The　results　show　that　nominal　shear　strength　size　effect　of　reinforced　concrete　beams　without　web　reinforcement　is　obvious,　and　CFRP　sheet　reinforcement　contributes　the　most　to　small-sized　beams.　The　effectiveness　decreases　with　an　increase　in　beam　size.　The　increase　of　fiber　ratio　improves　the　nominal　shear　strength　of　cantilever　beams,　but　it　also　weakens　the　size　effect　of　shear　strength.　When　the　fiber　ratio　is　high,　the　increase　of　peak　shear　stress　is　obviously　slowed　down,　that　is,　the　reinforcement　effect　is　not　obvious　when　an　overly　large　number　of　layers　are　used.　©　2019,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.