In　order　to　estimate　the　safety　of　the　RC　bridge　columns　with　hollow　section　under　biaxial　bending,　the　calculation　formulas　for　axial　compression　capacity　and　bending　moment　were　proposed　according　to　the　distribution　forms　of　neutral　axis　for　rectangular　RC　hollow　section　under　biaxial　bending.　The　3D　interaction　yield　surface　diagram　of　P-Mx-My　was　presented　by　numerical　simulation.　The　simplified　formula　for　ultimate　bearing　capacity　calculation　was　obtained　based　on　the　Bresler　ultimate　strength　theory　for　the　RC　bridge　columns　with　rectangular　hollow　section　with　axial　compression　ratio　less　than　0.3　and　under　biaxial　bending.　The　results　show　that　the　safety　check　result　obtained　by　the　3D　yield　surface　diagram　is　accordance　with　the　observed　experimental　phenomena　of　tested　RC　bridge　columns.　The　proposed　formula　is　proved　to　be　accurate　to　estimate　the　safety　of　rectangular　hollow　cross　section　under　biaxial　bending.