The　mechanical　behavior　of　reinforced　concrete　(RC)　beam-column　joints　with　different　sizes　under　cyclic　loads　at　varying　rates　was　investigated,　aiming　at　attaining　a　better　understanding　of　the　size　effect　and　strain　rate　effect　on　RC　beam-column　joints.　First,　a　2D　mesoscale　numerical　model　was　established　and　verified　by　existing　experimental　results.　Second,　numerical　tests　regarding　seismic　performances　of　RC　beam-column　joints　were　carried　out.　A　total　of　four　structural　sizes　and　five　strain　rates　were　taken　into　consideration.　The　damage　patterns,　hysteretic　curves,　skeleton　curves,　the　displacement　ductility,　the　stiffness　degradation,　and　the　shear　deformation　of　joints　under　different　working　conditions　were　analyzed.　Finally,　the　size　effect　and　strain　rate　effect　on　shear　resistance　and　shear　failure　mechanism　of　joints　were　discussed.　In　addition,　a　semitheoretical　formula　considering　structural　sizes　and　strain　rates　for　shear　strength　calculation　was　proposed　and　verified　by　available　experimental　data.