In　order　to　analyze　the　shear　size　effect　of　RC　beams　without　web　reinforcement　considering　debonding　of　CFRP　sheets,　a　three-dimensional　(3D)　meso-scale　numerical　analysis　model　of　CFRP-strengthened　reinforced　concrete　(RC)　beams　without　web　reinforcement　was　established,　which　considers　the　heterogeneity　of　concrete,　the　bond-slip　relationship　between　reinforcement　and　concrete,　and　the　interaction　between　CFRP　sheets　and　concrete.　On　the　basis　of　verifying　the　rationality　of　the　numerical　method,　meso-scale　models　of　28　CFRP-strengthened　RC　beams　were　designed　and　established.　The　effects　of　the　debonding　behavior　of　CFRP　sheets　on　the　shear　failure　behavior　and　size　effect　of　RC　beams　under　different　CFRP　fiber　ratios　(0.　0555%,　0.　1110%,　0.　2220%)　and　different　cross-section　sizes　(80　mm　×　200　mm,　160　mm　×　400　mm,　240　mm　×　600　mm　and　320　mm　×　800　mm)　were　analyzed.　The　analysis　results　show　that　considering　the　debonding　of　CFRP　sheets　can　truly　reflect　the　actual　shear　performance　of　RC　beams　in　the　state　of　imperfect　bonding　between　CFRP　sheets　and　concrete.　The　nominal　shear　strength　of　the　strengthened　beams　decreases　with　the　section　size,　showing　an　obvious　size　effect　phenomenon.　For　the　three　groups　of　fiber　ratios,　when　the　height　of　the　RC　beam　is　increased　from　200　mm　to　800　mm,　the　nominal　shear　strength　of　the　RC　beams　which　consider　CFRP　sheet　debonding　decreases　by　26.　5%,　17.　8%　and　13.　1%,　respectively,　while　those　not　considering　CFRP　sheet　debonding　decreases　by　20.　6%,　13.　0%　and　8.　1%,　respectively.　When　considering　the　debonding　behavior　of　CFRP　sheets,　the　weakening　effect　of　CFRP　sheets　on　the　shear　size　effect　of　RC　beams　is　not　significant.　Based　on　the　numerical　test　results　in　this　paper,　a　size　effect　law　of　shear　strength　of　CFRP-strengthened　RC　beams　without　web　bars　considering　the　debonding　of　CFRP　sheets　was　proposed.　The　theoretical　values　obtained　by　considering　the　debonding　of　CFRP　sheet　are　in　better　agreement　with　the　test　values,　which　on　the　one　hand　verifies　the　rationality　and　accuracy　of　the　extended　size　effect　law,　and　on　the　other　hand　indicates　that　the　debonding　of　CFRP　sheet　should　be　considered　in　the　practical　simulation.　©　2023　Science　Press.　All　rights　reserved.