This　paper　develops　a　nonlinear　model　for　the　analysis　of　circular　CFST　columns　under　equal　and　unequal　end　moments　using　fiber　beam　element　(FBE)　method.　An　iterative　process　adopting　Newton＇s　method　combined　with　secant　method　was　proposed　to　improve　the　calculation　efficiency.　A　test　database　was　collected　to　assess　the　accuracy　of　the　proposed　model　regarding　the　prediction　of　axial　load-bearing　capacity,　deflection　curves　and　load–deflection　curves.　The　verified　model　was　then　further　used　to　investigate　the　behavior　of　CFST　columns　under　different　end　moments.　It　was　found　that　the　normalized　sectional　locations　of　maximum　deflection　of　CFST　columns　are　only　significantly　affected　by　the　end　moment　ratio,　whereas　those　of　critical　sections　are　also　influenced　by　the　axial　load.　The　specimen　with　a　larger　end　moment　ratio,　steel　strength,　L/D　ratio　and/or　a　smaller　e1/D　ratio,　D/t　ratio　experiences　more　significant　second　order　effect.　The　bending　stiffness　of　CFST　columns　is　hardly　affected　by　the　end　moment　ratio.　Moreover,　the　current　codes,　i.e.,　EC4　and　AISC　360,　may　underestimate　the　capacities　of　CFST　columns　under　unequal　end　moments.　©　2023　Elsevier　Ltd