Studies　on　size　effect　around　deformation　performance　of　RC　members　are　carried　out　relatively　fewer　at　present.　This　article　evaluated　bending　deformation　capacity　and　size　effect　characteristics　of　RC　cantilever　beams　by　means　of　test　method.　And　decomposed　various　deformation　components　with　size　effect　factors　considered,　including　bending,　shear　and　bar-slip　deformation　and　so　on.　The　article　focus　on　discussing　bending　deformation　components　at　different　loading　stage　and　putting　forward　corresponding　distribution　functions.　Calculation　and　experimental　results　show　that　bending　deformation　characteristics　have　significant　differences　on　specimen　dimensions,　especially　in　nonlinear　loading　stage　after　longitudinal　reinforcement　yielding.　Large　size　members　have　a　significant　concrete　crushing　process.　ductility　reserves　show　a　growing　trend　with　specimens　size　increasing.　Bending　deformation　ability　depends　on　average　stiffness　along　overall　beam　before　longitudinal　reinforcement　yielding.　After　plastic　hinge　forming,　its　bending　performance　will　be　decided　by　average　stiffness　within　hinge　region　equivalent　length.