The　tests　of　9　composite　concrete-filled　square　thin-walled　steel　tubular　(CCFSTST)　columns　with　longitudinal　stiffeners　under　eccentric　compression　were　carried　out.　The　test　results　indicated　that　the　load-carrying　capacity　decreased　with　the　increase　of　eccentricity　and　slenderness　ratio,　but　increased　with　the　increase　of　core　concrete　strength.　Based　on　the　finite　element　model　verified　by　the　test　results,　the　working　mechanism　of　CCFSTST　columns　was　studied　and　the　parametric　analysis　was　conducted.　It　can　be　found　that　the　confinement　of　the　outer　steel　tube　is　focused　on　the　corners　of　the　cross-section,　the　majority　of　the　load　is　resisted　by　the　concrete　and　the　ductility　of　the　composite　column　is　enhanced　by　filling　core　concrete.　With　the　increase　of　the　steel　yield　strength,　steel　ratio　of　inner　concrete-filled　steel　tube　and　diameter　to　width　ratio,　the　abscissa　and　ordinate　values　of　the　equilibrium　point　in　the　relative　axial　compression　versus　relative　moment　relationship　decreased,　but　they　increased　with　the　increase　of　concrete　strength.　Meanwhile,　with　the　increase　of　slenderness　ratio,　the　axial　compression　versus　moment　relationship　trended　to　be　a　straight　line.　Finally,　the　simplified　model　was　proposed　to　predict　the　load-carrying　capacity　of　CCFSTST　columns　under　the　eccentric　compression.　©　2018,　Editorial　Department　of　Journal　of　Hunan　University.　All　right　reserved.