In　order　to　study　the　compression　behavior　of　pentagonal　shaped　CFST　mega-columns　in　a　high-rise　building,　experiments　on　six　1/5　scaled　specimens　were　carried　out.　There　were　four　different　types　of　specimens,　including　the　specimen　with　reinforcements　but　without　cavities,　the　specimen　with　cavities　but　without　reinforcements,　the　specimen　with　both　cavities　and　reinforcements,　the　specimen　with　reinforcements,　cavities　and　division　plates　and　vertical　ribs　which　were　cut　in　the　middle　of　the　column.　The　specimens　were　tested　under　axial　compression　or　eccentric　compression.　In　order　to　study　the　effect　of　the　repeat　loading　on　the　stiffness　degradation,　one-way　repeated　loading　test　was　adopted.　The　bearing　capacity,　stiffness　and　failure　characteristics　were　studied,　and　applicability　of　the　plane-section　assumption　was　analyzed.　Test　results　show,　with　regard　to　the　pentagonal　shaped　CFST　columns,　the　bearing　capacity　of　specimens　with　reinforcements　but　without　cavities　are　comparatively　poor;　compared　with　the　specimens　with　both　cavities　and　reinforcements,　the　bearing　capacity　of　specimens　without　reinforcements　is　almost　the　same,　but　the　bearing　capacity　decreases　rapidly　after　the　peak　load;　as　to　the　eccentric　compression　specimens,　compared　with　the　axial　compression　specimens　with　same　section,　the　bearing　capacity　is　lower　and　stiffness　degradation　is　slower;　as　to　the　specimen　where　the　cavity　plates　and　vertical　rib　are　cut　in　the　middle,　the　stiffness　mutation　is　confirmed.　The　horizontal　and　vertical　division　plates　can　improve　the　stability　of　the　outer　plate　significantly.　The　section　deformation　essentially　agrees　with　the　plane-section　assumption.