This　paper　develops　a　fiber-based　model　for　rectangular/square　concrete-filled　steel　tube　(CFST)　columns　under　arbitrary　end　moments　considering　the　member　imperfection.　The　accuracy　of　the　proposed　model　regarding　the　prediction　of　capacity,　deflection　curves　and　full　range　curves　is　verified　using　a　collected　test　database.　The　verified　model　is　further　used　to　investigate　the　behaviour　of　rectangular/square　CFST　columns　under　arbitrary　end　moments.　It　was　found　that　the　varying　trends　of　strength　and　deformation　capacity　of　rectangular/square　CFST　columns　under　arbitrary　end　moments　are　opposite　while　increasing　the　end　moment　ratio　beta　,　L/r　ratio　and　f　c　,　whereas　those　are　the　same　if　increasing　b/t　ratio　and　f　y　.　Higher　f　y　and/or　smaller　b/t　ratio　may　be　adopted　in　order　to　achieve　larger　strength　and　deformation　capacity　simultaneously.　The　location　of　maximum　deflection　at　peak　state　h　kp　/　L　is　only　significantly　affected　by　end　moment　ratio　beta　,　whereas　the　location　of　critical　section　at　peak　state　h　cp　/　L　is　significantly　affected　by　end　moment　ratio　beta　,　L　/　r　ratio　and　yield　strength　f　y　.　Moreover,　current　design　codes,　i.e.,　EC4,　AISC　360　and　GB50936-2014,　were　found　to　poorly　predict　the　resistance　to　axial　load　and　bending　moment　of　rectangular/square　CFST　columns　under　arbitrary　end　moments.