The　purpose　of　this　study　is　to　investigate　the　size　effect　on　reinforcement　concrete　(RC)　shear　walls　having　different　shear　span　ratios　and　vertical　reinforcement　ratios　by　the　two-dimensional　(2D)　meso-scale　simulation　method.　Firstly,　the　meso-scale　simulation　method　was　verified　by　the　existing　test　data.　Then,　the　effects　of　shear　span　ratio　and　vertical　reinforcement　ratio　on　the　mechanical　properties　of　RC　shear　walls　with　different　structure　sizes　were　studied　by　using　this　method.　The　results　show　that:　1)　The　failure　mode　of　shear　walls　changes　from　shear　failure　to　bending　failure　with　the　increase　of　the　shear　span　ratio.　2)　With　the　increase　of　the　shear　span　ratio,　the　shear　capacity　of　the　shear　wall　decreases　and　the　ductility　increases,　which　leads　to　the　weakening　of　the　size　effect.　3)　The　increase　of　the　vertical　reinforcement　ratio　has　a　slight　increase　in　the　shear　capacity　of　the　shear　wall,　but　has　almost　no　effect　on　the　ductility　and　size　effect.　In　addition,　based　on　the　established　size　effect　law　which　can　reflect　the　quantitative　effect　of　horizontal　reinforcement　ratio　and　axial　compression　ratio,　a　new　size　effect　law　for　RC　shear　wall　was　proposed　considering　the　quantitative　effect　of　shear　span　ratio.