In　order　to　meet　the　need　of　the　study　on　the　tunnel　fire　safety　system,　taking　the　tunnel　laboratory　bench　in　the　key　laboratory　of　the　university　of　science　and　technology　of　China　as　the　object,　this　paper　does　a　scale　model　experiment　on　the　tunnel　fire,　and　uses　the　Fire　Dynamics　Simulator　(FDS)　software　to　simulate　fire　smoke　layer　velocity　under　different　longitudinal　ventilation　control,　by　comparing　the　experimental　and　simulation　results,　this　paper　not　only　gives　the　variation　law　of　the　tunnel　fire　smoke　layer　velocity　under　different　longitudinal　ventilation　speed,　but　also　proposes　the　concept　of　the　smoke　stratification　critical　wind　speed,　which　will　provide　some　references　for　the　road　tunnel　fire　control,　rescue　and　evacuation.