To　study　the　initial　failure　and　collapse　mechanisms　of　interior　column　failure　for　multi-story　steel　structures　under　fire,　tests　of　two　full　scale　steel　frame　structure　were　performed.　The　temperature　distribution　and　displacement　response　of　the　column　and　beam　were　obtained,　and　the　variation　of　axial　force　of　the　interior　column　was　obtained　using　the　force-measuring　bearing.　Based　on　the　finite　element　analysis　and　test　results,　collapse　mechanism　of　steel　structures　induced　by　the　interior　heated　column　was　analyzed,　and　column　buckling　temperature,　column　failure　temperature,　and　structural　failure　temperature　were　defined.　The　results　show　that　bending　failure　occurs　in　the　weak　axis　direction　for　the　column　under　high　temperature.　Local　buckling　failure　occurs　at　the　heated　column　below　the　fire-protected　joint.　Buckling　failure　of　the　interior　column　leads　to　failure　of　all　the　upper　connected　beams.　Failure　of　a　column　in　a　structure　does　not　mean　the　collapse　of　the　structure.　The　column　buckling　temperature　and　column　failure　temperature　decrease　with　the　increase　of　the　load　level.　©,　2015,　Science　Press.　All　right　reserved.