A　method　is　presented　to　predict　the　complete　stress-strain　curves　of　concrete　subjected　to　triaxial　stresses,　which　were　caused　by　axial　load　and　lateral　force.　The　stress　can　be　induced　due　to　the　confinement　action　inside　a　special-shaped　steel　tube　having　multiple　cavities.　The　existing　reinforced　confined　concrete　formulas　have　been　improved　to　determine　the　confinement　action.　The　influence　of　cross-sectional　shape,　of　cavity　construction,　of　stiffening　ribs　and　of　reinforcement　in　cavities　has　been　considered　in　the　model.　The　parameters　of　the　model　are　determined　on　the　basis　of　experimental　results　of　an　axial　compression　test　for　two　different　kinds　of　special-shaped　concrete　filled　steel　tube　(CFT)　columns　with　multiple　cavities.　The　complete　load-strain　curves　of　the　special-shaped　CFT　columns　are　estimated.　The　predicted　concrete　strength　and　the　post-peak　behavior　are　found　to　show　good　agreement　within　the　accepted　limits,　compared　with　the　experimental　results.　In　addition,　the　parameters　of　proposed　model　are　taken　from　two　kinds　of　totally　different　CFT　columns,　so　that　it　can　be　concluded　that　this　model　is　also　applicable　to　concrete　confined　by　other　special-shaped　steel　tubes.