Based　on　ABAQUS　finite　element　numerical　calculation　platform,　considering　the　heterogeneity　of　concrete　materials　and　the　strain　rate　effect　of　reinforcement　and　concrete,　a　three-dimensional　(3D)　meso-scale　numerical　analysis　model　of　Reinforced　Concrete　(RC)　beam　was　established,　and　then　the　shear　performance　and　size　effect　of　RC　beams　under　different　strain　rates　and　stirrup　ratios　were　investigated.　The　results　show　that:　1)　With　the　increase　of　strain　rate　and　stirrup　ratio,　the　shear　bearing　capacity　will　increase　to　varying　degrees.　2)　The　nominal　shear　strength　decreases　with　the　increase　of　beam　height,　and　there　is　a　significant　size　effect　phenomenon.　3)　The　increase　of　strain　rate　and　stirrup　ratio　can　both　increase　the　nominal　shear　strength　of　RC　beams　and　weaken　the　size　effect　of　nominal　shear　strength.　4)　The　proposed　static/dynamic　shear　uniform　size　effect　law　of　RC　beams　considers　the　influence　of　size　effect,　strain　rate　effect　and　stirrup　ratio　at　the　same　time,　which　can　well　predict　the　nominal　shear　strength　of　RC　beams　under　static　and　dynamic　loads,　with　certain　accuracy　and　rationality.　©　2023　Chinese　Vibration　Engineering　Society.　All　rights　reserved.