To　research　the　flexural　performance　of　ultra-high　performance　concrete　(UHPC)　filled　high-strength　steel　tube　(UHPCFST)　and　UHPC　filled　double　skin　high-strength　steel　tube　(UHPCFDST)　under　bending　load,　an　experimental　investigation　was　presented.　In　this　paper,　four　UHPCFST　specimens,　one　UHPCFDST　with　square　tube　inner　specimen　and　three　UHPCFDST　with　circular　tube　inner　specimens　were　designed　to　evaluate　the　influence　of　steel　ratio,　steel　yield　strength,　and　cross-section　combination　form　on　the　flexural　performance　of　the　specimens.　Experimental　results　indicated　that　the　composite　action　between　UHPC　and　high-strength　steel　tube　was　efficient,　all　specimens　showed　ductile　failure　under　pure　bending　load.　As　the　steel　ratio　and　steel　yield　strength　increased,　the　ultimate　flexural　capacity　of　specimens　significantly　increased,　but　the　changes　of　flexural　stiffness　were　not　obvious.　The　results　also　demonstrated　that　when　the　hollow　section　ratio　was　0.535　to　0.567,　the　UHPCFDST　with　circular　tube　inner　specimens　had　higher　ultimate　flexural　capacity　and　ductility　than　the　UHPCFST　specimens.　Compared　with　square　inner　tube,　when　the　steel　ratio　was　the　same,　circular　inner　tube　was　recommended　for　UHPCFDST　specimens.　An　analytical　model　of　ultimate　flexural　capacity　for　UHPCFST　and　UHPCFDST　specimens　was　proposed.　Compared　with　the　three　current　codes,　the　accuracy　of　the　model　was　proved.