To　improve　the　compression　performance　and　ductility　of　rectangular　concrete-filled　steel　tube　(CFST)　columns　with　large　dimensions,　longitudinal　stiffeners,　horizontal　tie　bars,　studs,　internal　diaphragms,　and　steel　re-inforcement　cages,　were　set　inside　the　columns.　Six　CFST　column　specimens　with　different　construction　characteristics　were　designed　and　tested　under　repeated　uniaxial　compression　loading,　Test　samples　were　extracted　from　the　rectangular　cavities　at　the　two　ends　and　along　the　long　axis　of　the　mega-column　from　China　Zun　Tower.　The　hysteretic　curves,　skeleton　curves,　energy　dissipation　capacity,　bearing　capacity,　stiffness　and　strain　of　specimens,　and　the　effect　on　the　axial　compression　performance　based　on　different　construction　characteristics　are　herein　discussed　and　clarified.　Based　on　the　conducted　tests　on　these　columns,　a　bearing　capacity　calculation　method　is　proposed.　The　test　results　indicate　that　the　longitudinal　stiffeners　set　inside　the　CFST　columns　facilitate　the　sharing　of　axial　forces　and　strengthen　the　stiffness,　bearing　capacity,　and　ductility.　The　horizontal　tie　bars　help　the　improvement　of　the　constraint　of　the　concrete　at　loads　higher　than　the　ultimate　load.　Welding　studs　on　the　inner　surface　of　the　steel　tubes　help　to　strengthen　co-operative　work　between　the　steel　tubes　and　the　concrete　upon　application　of　the　ultimate　load.　Setting　internal　diaphragms　inside　CFST　columns　can　enhance　the　ultimate　bearing　capacity　and　energy　dissipation　significantly.　The　setting　of　steel　reinforcement　cages　inside　the　CFST　columns　stabilizes　the　mechanical　performance　manifested　by　the　significant　improvements　in　the　ultimate　bearing　capacity　and　ductility.