In　order　to　analyze　and　simulate　the　response　and　collapse　of　multi-story　reinforced　concrete　frame　structures　under　fire,　a　novel　numerical　model　based　on　the　fiber　beam　model　was　proposed　in　this　paper.　By　dividing　the　cross　section　of　beam　element　into　many　small　concrete　and　steel　fibers,　this　model　could　consider　the　non-uniform　temperature　distribution　across　the　section　and　simulate　the　behavior　of　material　nonlinearity　and　geometry　nonlinearity.　This　fiber　model　was　validated　by　comparing　with　experimental　results　from　a　one-story,　one-bay　frame　fire　test.　Then,　the　response　and　collapse　process　of　a　multi-story　reinforced　concrete　structure　were　analyzed　and　the　influence　of　different　fire　scenarios　were　discussed.　It　can　be　concluded　that　the　proposed　fiber　model　can　be　used　to　simulate　the　collapse　process　of　reinforced　concrete　frames　under　fire,　and　different　fire　scenarios　lead　to　different　collapse　mechanisms.　It　is　found　that　the　spreading　fire　may　cause　more　severely　damage　to　multi-story　reinforced　concrete　structures　than　the　fire　without　spread.　The　results　provide　a　useful　reference　for　practical　fire　resist　design　for　structures　under　fire.