Analysis　on　size　effect　of　calculation　theory　for　ultimate　bearing　capacity　of　flexural　member　is　carried　out　in　this　paper,　including　basic　assumptions　and　calculation　equations.　The　paper　collects　test　information　of　five　different　section　size　samples　in　the　state　of　ultimate　bearing　capacity,　including　sectional　bending　moment,　deflection　and　section　strain　etc.　The　total　number　of　RC　free　beam　specimens　is　13.　In　research　scale,　rationalities　of　basic　assumptions　are　verified,　influences　on　size　effect　of　concrete　materials　are　evaluated,　characteristic　parameters　are　measured　and　derived　with　size　changing,　and　safety　of　calculation　theory　about　ultimate　bearing　capacity　of　flexural　members　is　basically　verified.　It　is　also　found　that　security　reserve　of　calculation　theory　shows　a　trend　of　decrease　with　specimen　size　increasing.　As　for　large-size　flexural　members,　code　value　of　ultimate　strain　under　non-uniform　compression　is　bigger　than　test　value.　Strength　and　deformation　capacity　of　concrete　materials　under　compression　zone　is　becoming　smaller　with　specimen　size　increasing.　©　2011　IEEE.