An　experimental　investigation　on　axial　compression　performance　of　7　ultra-high　performance　concrete　(UHPC)　filled　high　strength　steel　tubular　(UFHST)　columns　(1　020　MPa　steel　yield　strength　and　147　MPa　concrete　strength)　was　conducted.　Test　results　show　that:　with　the　increase　of　length-to-diameter　ratio　(3-18),　the　second-order　effect　caused　by　the　initial　imperfection　becomes　more　significant,　the　bearing　capacity　of　composite　column　decreases,　the　utilized　degree　of　material　strength　is　reduced,　and　the　failure　mode　changes　from　the　compression　strength　failure　to　the　instability　bending　failure.　Furthermore,　the　accuracy　of　finite　element　model　(FEM)　has　been　verified　by　experimental　results,　and　the　range　of　parametric　analysis　for　length-to-diameter　ratio　was　extended　by　using　FEM.　In　addition,　the　Comparison　of　the　values　calculated　using　Chinese　codes　and　the　valued　obtained　from　finite　element　analyses　was　performed.　It　shows　that　the　current　calculation　methods　have　a　relatively　poor　accuracy　for　predicting　the　stability　coefficient　of　UFHST　columns　under　axial　compression.　Thus,　the　calculation　method　with　poor　accuracy　has　been　modified,　and　its　prediction　agrees　well　with　the　results　calculated　by　FEM.　©　2019,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.