By　using　the　finite　element　method,　the　relationship　between　temperature　variation　and　debonding　of　CFST　section　was　analyzed.　The　analysis　result　shows　that　debonding　may　easily　happen　in　CFST　columns　when　exposed　to　fire.　Whether　Debonding　or　not　depends　on　the　thickness　of　anti-fire　layer,　section　dimension　and　fire　duration.　The　thickness　of　anti-fire　layer　has　great　influence　on　the　initial　debonding　gap　width.　For　the　usually　used　CFST　column　without　anti-fire　layer,　the　gap　width　is　0.33　mm　to　2.04　mm.　For　the　CFST　column　with　anti-fire　layer,　the　gap　width　is　0.87　mm　to　9.24　mm.　The　temperature　of　steel　tube　is　higher　and　the　temperature　of　concrete　is　lower　in　the　debonded　CFST　sections　than　that　in　bonded　ones.　Compared　with　the　case　of　no　anti-fire　layer,　debonding　has　much　influence　on　the　temperature　change　of　CFST　column　with　anti-fire　layer.　The　debonding　gap　width　increase　along　with　the　increase　of　fire　lasting　time.　The　bigger　the　diameter　is,　the　wider　the　gap　is.　The　debonding　gap　width　is　also　influenced　by　the　anti-fire　layer.　The　final　debonding　gap　width　of　the　specimen　with　anti-fire　layer　is　less　than　that　of　the　specimen　without　anti-fire　layer.