The　existing　theoretical　models　for　the　analysis　of　concrete-filled　steel　tube　(CFST)　columns　are　mainly　limited　to　circular　specimens.　This　paper　is　aimed　at　developing　a　unified　theoretical　model　which　is　applicable　to　CFST　columns　with　different　cross-sectional　shapes,　including　circular,　square,　rectangular　and　round-ended　specimens.　CFST　columns　with　different　shapes　(original　columns)　were　replaced　with　equivalent　circular　columns　by　assuming　that　they　have　the　same　sectional　areas　of　core　concrete　and　steel　tube.　The　difference　in　the　behavior　between　the　original　and　equivalent　CFST　columns　is　attributed　to　the　shape　effect,　which　is　indicated　and　modelled　by　a　confinement　effectiveness　factor.　Then,　a　unified　theoretical　model　for　axially　loaded　CFST　columns　with　different　cross-sectional　shapes　was　developed　based　on　an　equivalent　circular　column　with　the　shape　effect　considered.　A　total　of　982　CFST　columns,　including　550　circular　columns,　396　rectangular　(and　square)　columns,　and　36　round-ended　columns,　were　collected　to　assess　the　proposed　model.　Results　suggest　that　the　proposed　model　is　capable　of　accurately　predicting　the　load-carrying　capacity　and　load-deflection　curves　of　CFST　columns　with　different　cross-sectional　shapes.　Finally,　the　proposed　theoretical　model　was　adopted　to　develop　a　unified　design　model　of　axial　load-carrying　capacity.