In　order　to　study　the　shear　performance　and　size　effect　behavior　of　reinforced　concrete　(RC)　beams　with　minimum　stirrup　ratio,　the　shear　failure　test　of　six　RC　beams　with　minimum　stirrup　ratio　under　concentrated　load　was　completed,　and　the　shear　failure　modes　and　failure　mechanisms　were　studied.　The　influence　of　structure　size　on　shear　force-deflection　curve,　oblique　crack　width,　concrete　strain,　longitudinal　reinforcement　strain　and　stirrup　strain　of　RC　beams　was　analyzed,　and　the　size　effect　law　of　nominal　shear　strength　of　RC　beams　with　minimum　stirrup　ratio　was　revealed　quantitatively.　The　results　show　that　the　nominal　shear　strength　of　RC　beams　with　minimum　stirrup　ratio　exists　size　effect.　With　the　increase　of　beam　height,　the　number　of　cracks　increases,　the　width　of　oblique　cracks　increases,　the　corresponding　tensile　strain　of　concrete　increases,　the　strain　of　stirrup　increases,　and　the　strain　of　longitudinal　reinforcement　decreases.　The　theoretical　formula　of　size　effect,　which　established　on　the　basis　of　the　numerical　simulation　results　in　the　early　stage,　was　accorded　with　the　experimental　results　in　this　paper,which　the　error　is　less　than　20%　.　It　can　quantitatively　describe　the　influence　of　structural　size　on　the　nominal　shear　strength　of　RC　beams　with　minimum　stirrup　ratio.　The　modified　formula　of　code　suggested　in　this　paper　can　better　reflect　the　effect　of　structural　size　on　the　shear　bearing　capacity　of　RC　beams　with　minimum　stirrup　ratio.　©　2023　Science　Press.　All　rights　reserved.