U-rib　stiffened　plate　is　the　main　bearing　members　of　the　top　and　bottom　flanges　of　a　steel　box　girder.　The　local　buckling　of　U-rib　web　and　the　stiffened　plate　are　the　two　main　failure　modes.　To　study　the　local　stability　performance　of　U-rib　stiffened　plate,　two　specimens　of　U-rib　web　and　stiffened　plate　were　designed　and　manufactured,　where　ratio　of　width　to　thickness　of　U-rib　web　and　stiffened　plate　as　well　as　the　bending　radius　between　U-rib　flange　and　web　are　the　main　parameters.　Through　the　compression　test,　local　buckling　failure　mode,　the　stability　bearing　capacity,　stress-displacement　curve　and　local　stability　reduction　factor　of　the　specimens　were　obtained.　Experimental　results　show　that:　with　the　increase　of　ratio　of　width　to　thickness　of　local　plate　member,　the　failure　mode　of　specimen　will　be　changed　from　strength　failure　into　buckling,　and　the　buckling　failure　characteristics　turn　to　be　more　and　more　obvious.　When　the　ratio　of　width　to　thickness　of　plate　member　is　greater　than　22.5,　the　plate　member　would　be　instability　earlier　than　other　members.　With　the　increase　of　the　bending　radius　between　U-rib　flange　and　web,　the　width　of　the　web　and　its　ratio　of　width　to　thickness　will　be　larger,　which　will　result　in　the　decrease　of　U-rib＇s　stability　bearing　capacity.　Comparing　the　test　results　with　the　stability　coefficient　curve　of　the　China　design　specification　on　highway　steel　bridges,　it　can　be　seen　that　using　yield　strength　to　calculate　the　local　stability　reduction　factor,　the　calculated　plate＇s　stability　bearing　capacity　is　obviously　less　than　the　experimental　value;　while　using　ultimate　strength　to　calculate　the　local　stability　reduction　factor,　the　calculated　plate＇s　stability　bearing　capacity　is　close　to　the　experimental　value.　It　is　shown　that　the　safety　factor　will　be　equal　to　the　ratio　of　ultimate　strength　to　yield　strength,　when　using　the　steel　bridge　specification　to　calculate　the　stability　bearing　capacity　of　the　U-rib　stiffened　plate.　©　2017,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.