ABS　T　R　A　C　T　Drop　hammer　impact　tests　based　on　the　reduced-scale　model　are　the　most　commonly　accepted　technique　to　investigate　the　impact　response　of　reinforced　concrete　(RC)　beams.　However,　the　scale　of　RC　beam　prototypes　in　actual　engineering　is　much　larger　than　that　of　test　specimens　in　the　laboratory.　Whether　the　analytical　results　obtained　from　the　small-scaled　specimens　can　be　fully　extrapolated　and　evolved　to　large/full-scaled　geometri-cally　similar　prototype　components　needs　further　discussion.　Given　a　structural　scale　factor,　this　study　applied　numerical　simulations　on　four　series　of　geometrically　similar　RC　beams　under　different　impact　energy　combi-nations.　The　effects　of　structural　scales　and　energy　combinations　on　the　beams＇　damage　modes,　midspan　displacement　response,　and　energy　absorption　were　numerically　investigated.　The　results　indicate　that　there　is　a　scaling　effect　on　the　impact　displacement　of　geometrically　similar　RC　beams,　which　is　influenced　by　the　energy　combination.　A　dimensionless　displacement　analytical　model　was　developed　for　single-scaled　RC　beams　under　drop　weight　impact　using　Buckingham＇s　&　pi;-theorem,　and　it　was　validated　by　several　drop　weight　impact　results.　Then,　a　unified　impact　displacement　prediction　model　for　geometrically　similar　RC　beams　was　proposed　by　considering　the　coupling　effect　of　structural　scales　and　impact　energy　combinations.　Moreover,　the　numerical　parametric　study　results　preliminarily　evaluated　the　accuracy　and　safety　of　the　present　model.　It＇s　worth　stating　that　the　proposed　model　provides　a　reference　for　designing　and　verifying　the　prototype　members.