Rail　transit　hub　is　key　node　in　urban　transportation　system.　The　study　on　properties　of　ventilation　and　smoke　control　system　can　improve　response　ability　in　case　of　fire　and　give　ventilation　and　smoke　control　design　guidance　for　underground　rail　transit　hub.　Take　Beijing　DongZhimen　underground　rail　transit　hub　as　research　object,　according　to　its　air　turbulent　flow　characteristics,　introducing　standard　turbulence　model　based　on　the　N-S　equation.　Build　the　computational　fluid　dynamics　model　for　solving　the　flow　field　within　underground　rail　transit　hub.　Through　theoretical　analysis　and　numerical　simulation,　take　＂Siamese　model＂　results　as　the　boundary　condition　and　establish　a　mathematical　model　of　rail　transit　hub　with　CFX.　Then　research　fire　smoke　development　and　spread　laws　when　the　exhaust　fan　within　underground　rail　transit　hub　delayed　open.