For　accurately　simulating　the　dynamic　mechanical　behavior　of　Reinforced　Concrete　(RC)　shear　walls　subjected　to　dynamic　loads,　in　this　paper,　a　two-dimensional　meso-scale　numerical　model　is　proposed　to　capture　the　heter-ogenous　nature　and　strain　rate　effect　of　concrete　structure.　The　impacts　of　shear　span　ratio　and　strain　rate　on　the　dynamic　mechanical　properties　and　size　effect　law　of　the　RC　shear　walls　are　investigated.　The　results　indicate　that:　1)　the　bearing　capacity,　ductility,　and　energy　dissipation　capacity　of　the　RC　shear　walls　increase　with　an　increasing　strain　rate;　2)　the　failure　mode　of　the　RC　shear　walls　is　affected　by　the　shear　span　ratio,　while　the　bearing　capacity　decreases　with　an　increasing　shear　span　ratio;　3)　both　the　increased　strain　rate　and　shear　span　ratio　weaken　the　size　effect　of　the　RC　shear　wall.　Based　on　these　results,　the　dynamic　size　effect　formula　of　the　RC　shear　wall　is　proposed　to　quantitatively　describe　the　influence　of　strain　rate　on　the　size　effect.　The　proposed　formula　is　validated　by　comparing　both　simulation　and　experimental　results.