Coarse　aggregate　is　an　important　proportion　of　concrete　material,　and　the　change　of　its　size　will　affect　the　contribution　of　aggregate　interlock　behaviour　in　concrete　beams　to　shear　capacity.　In　order　to　consider　the　effect　of　the　coarse　aggregate　size　on　the　shear　failure　of　Basalt　Fiber　Reinforced　Polymer　(BFRP)　beams　without　stirrup　systematically,　the　meso-scale　simulation　was　selected　and　a　numerical　model　of　BFRP　reinforced　concrete　beams　without　stirrup　was　established.　The　effects　of　member　size　and　coarse　aggregate　size　on　the　shear　failure　mode　and　shear　strength　of　BFRP　reinforced　concrete　beams　were　simulated　and　analyzed.　The　results　show　that　the　size　effect　exists　in　the　shear　strength　of　BFRP　reinforced　concrete　beams　without　stirrup.　Meanwhile,　the　increase　of　the　maximum　aggregate　size　improves　the　shear　capacity　of　concrete　beam,　and　weakens　the　size　effect　of　shear　strength.　According　to　the　influence　mechanism　and　law　of　maximum　coarse　aggregate　size,　theoretical　formula　of　size　effect　on　the　shear　strength　of　BFRP　reinforced　concrete　beams　was　established　on　the　basis　of　Fracture-SEL,　and　its　accuracy　and　rationality　are　verified　via　experimental　data.　©　2023　China　National　Publications　Import　and　Export　(Group)　Corporation.　All　rights　reserved.