The　shear-span　ratio　has　an　important　influence　on　the　crack　development　and　on　the　failure　mode　of　reinforced　concrete　(RC)　beams　strengthened　with　carbon　fiber　reinforced　polymer　(CFRP).　However,　there　were　few　studies　on　the　effects　of　its　shear　strength　and　size　effect.　A　mechanical　analysis　model　for　shear　failure　of　reinforced　concrete　beams　strengthened　with　CFRP　was　established　by　using　three-dimensional　numerical　meso-scale　simulation　method,　considering　the　meso-heterogeneity　of　the　concrete　and　the　interaction　between　the　CFRP　and　concrete.　Based　on　the　verification　of　the　rationality　of　the　meso-scale　method,　the　influence　mechanism　and　law　of　the　shear-span　ratio　on　the　shear　failure　and　size　effect　of　CFRP-strengthened　RC　beams　were　simulated　and　analyzed.　The　results　show　that:　the　shear-span　ratio　has　a　great　influence　on　the　shear　failure　mode　of　the　strengthened　beam,　and　the　larger　the　shear-span　ratio,　the　closer　the　beam　is　to　the　cable-stayed　failure　with　better　ductility.　The　shear-span　ratio　had　better　shear　capacity　for　CFRP-strengthened　beams　and　the　influence　on　the　size　effect　of　shear　strength　was　small.　The　shear-span　ratio　has　a　greater　influence　on　the　CFRP　shear　contribution　in　the　strengthened　beam.　The　larger　the　shear-span　ratio,　the　better　the　shear　effect　of　CFRP　on　strengthened　beams.　The　beam　reinforcement　effect　of　the　shear-span　ratio　(λ　=　2.5)　is　most　effective.　Copyright　©2021　Engineering　Mechanics.　All　rights　reserved.