This　study　takes　a　Beijing　subway　station　as　the　calculation　object,　makes　the　calculation　results　of　the　SES　software　as　the　boundary　conditions　in　the　FLUNET　software　simulation　process　and　uses　the　method　of　combining　the　field　measurement　and　numerical　calculation,　to　study　the　flow　characteristics　of　the　outdoor　fresh　air　which　is　introduced　through　the　ground　entrance-exits　based　on　the　piston　effect　in　the　station.　Study　results　show　that:　the　fresh　air　volume　introduced　through　the　ground　entrance-exits　that　based　on　the　piston　effect　can　basically　meet　the　fresh　air　demand　for　3837　people　on　the　platform　in　off-peak　hour.