Analysis　and　calculation　methods　of　reinforced　concrete　structure　at　present　are　based　on　test　results　of　small-size　component.　This　paper　carried　out　test　research　on　size　effect　of　flexural　capacity　of　RC　cantilever　beams.　Sectional　height　of　the　biggest　experimental　specimen　is　1000　mm.　Obtaining　detailed　test　data　during　different　loading　stage,　such　as　carrying　capacity,　deflection,　steel　and　concrete　strain　etc.　Through　observing　test　phenomenon　and　analyzing　test　data,　verifying　the　safety　to　calculation　formulas　for　ultimate　bearing　capacity　of　flexural　members.　Strength　and　ductility　reserves　show　a　growing　trend　with　specimen　size　increasing.