With　the　development　of　the　subway,　the　energy　consumption　of　subway　ventilation　and　air-conditioning　systems　is　increasing　rapidly.　To　solve　this　problem,　this　paper　describes　the　environment　of　a　subway　station　in　Beijing　subway　line　no.　2　from　July　to　September,　2011,　and　uses　numerical　methods　to　quantitatively　analyze　and　evaluate　the　contributions　of　the　subway　piston　effect　and　natural　outdoor　cold　sources　to　energy　saving　in　the　air-conditioning　system　and　improvement　of　the　subway　environment.　The　results　show　that　the　piston　effect　can　be　used　for　ventilation　in　each　area　of　the　subway　station.　During　summer,　part　of　the　subway　air-conditioning　season,　a　natural　cold　source　can　introduce　a　cold　capacity　of　5,100GJ　to　the　subway　station.