The　failure　of　reinforced　concrete　(RC)　members　is　closely　associated　with　the　mesoscopic　structure　of　concrete.　To　describe　the　complicated　failure　process　of　RC　beams　subjected　to　impact　loads　accurately,　a　3D　mesoscopic　simulation　method　considering　the　concrete　hetero-geneities　was　developed.　At　the　meso-scale,　the　concrete　was　assumed　to　be　composed　of　aggregate,　mortar　matrix　and　the　interfacial　transition　zones　(ITZ).　In　the　simulation　method,　the　strain　rate　effects　for　the　three　meso-components　and　steel　bars　were　taken　into　account,　and　the　web　reinforcement　was　simply　embedded　into　the　plane　concrete　members　without　considering　the　bond-slip　behavior.　The　mesoscopic　simulation　method　was　validated　and　verified　by　comparing　the　simulation　results　with　Fujikake　et　al.＇s　test　observations　and　macro-scale　simulation　results　in　terms　of　failure　pattern,　impact　force　and　mid-span　deflection.　Moreover,　the　impact　responses　of　the　RC　beams　involving　the　acceleration　and　velocity　distribution　as　well　as　the　impact　stress　distribution　were　also　investigated.　Finally,　based　on　the　mesoscopic　simulation　method,　the　influences　of　stirrup　ratio,　hammer　weight　and　span　length　on　the　impact　behavior　of　RC　beams　were　studied　and　discussed.