To　understand　the　mechanical　behavior　of　composite　structures　with　high　strength　materials,　seven　ultra-high　strength　concrete　(UHSC)　filled　high　strength　steel　tube　(CuFShT)　columns　under　axial　load　were　tested.　The　failure　modes,　load-axial　displacement　curves,　load-deflection　curves,　and　steel　strains　of　the　specimens　with　different　length　to　diameter　(L/D)　ratios　were　investigated.　The　results　show　that　the　influence　mechanism　of　the　L/D　ratio　on　the　overall　buckling　of　CuFShT　columns　is　similar　to　that　on　ordinary　CFST　columns.　However,　the　CuFShT　columns　exhibited　sudden　bending　behavior　earlier　due　to　the　significant　elastic　behavior　of　its　composite　materials.　A　finite　element　model　verified　by　the　test　results　was　used　to　explore　the　influence　of　section　parameters　on　the　stability　curves.　The　results　indicate　that　the　influence　is　negligible　if　the　slenderness　ratio　is　regularized　by　the　column　strength.　The　column　strength　is　influenced　by　the　difference　in　the　confinement　action　of　different　material　combinations.　Taking　the　regularized　slenderness　ratio　as　an　independent　variable,　a　new　calculation　method　of　the　stability　coefficient　with　an　extensive　application　scope　was　proposed.　It　has　good　accuracy　in　predicting　the　strengths　of　CuFShT　columns　under　axial　load.　Copyright　©2022　Engineering　Mechanics.　All　rights　reserved.