Eight　composite　concrete-filled　square　thin-walled　steel　tubular　(CCFSTST)　slender　columns　under　axial　compression　were　designed　and　fabricated.　Through　the　experiments,　the　effects　of　the　slenderness　ratio　and　the　cross-sectional　type　on　axial　compressive　resistance　of　CCFSTST　slender　columns　were　studied.　The　test　results　indicate　that　the　resistance　of　the　column　is　reduced　with　the　increasing　of　the　slenderness　ratio.　Through　embedding　high-strength　concrete-filled　circular　steel　tube,　the　resistance　of　the　composite　column　is　improved　by　33%.　After　embedding　a　circular　steel　hollow　tube,　the　resistance　of　the　composite　column　is　reduced　by　14%.　The　CCFSTST　slender　columns　with　a　solid　cross-section　exhibit　higher　residual　load-carrying　capacity　and　ductility.　Based　on　the　ABAQUS　and　the　relative　constitutive　models,　the　finite　element　(FE)　models　of　CCFSTST　slender　columns　were　developed.　The　predicted　results　agreed　well　with　the　test　results.　Based　on　the　FE　model,　the　mechanical　behavior　analysis　and　parametric　analysis　were　carried　out.　The　analysis　indicates　that　the　influences　of　the　welding　residual　stress　and　cold-forming　on　the　axial　compressive　resistance　are　less　than　1.5%.　Meanwhile　the　above　influences　are　offset.　Thus,　they　can　be　ignored　for　the　behavior　analysis.　With　the　increasing　of　the　yield　strength　of　the　inner　steel　tube,　concrete　strength　or　diameter　to　width　ratio,　the　stability　coefficients　of　the　CCFSTST　slender　column　with　a　solid　cross-section　are　decreased.　The　simplified　model　was　proposed　to　predict　the　axial　compressive　resistance　of　CCFSTST　slender　columns.　The　predictions　agreed　well　with　the　test　results.　©　2017,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.