In　order　to　determine　the　optimal　parameters　of　the　external　insulation　system　and　guide　the　energy　saving　and　greenhouse　gas　emission　reduction　of　building,　a　typical　student　dormitory　building　in　Beijing　was　chosen　as　research　object.　The　life　cycle　thinking　and　dynamic　simulation　method　were　used　in　the　present　investigation.　The　relationship　between　the　expandable　polystyrene　(EPS)　external　insulation　system　design　parameters　and　building　energy　consumption　and　greenhouse　gas　emission　in　each　phase　of　materials　production　phase,　operation　phase　and　the　whole　life　cycle　was　studied,　systematically.　The　results　show　that　the　consumption　of　clay　brick,　concrete　and　cement　mortar　account　for　98.1%　of　the　total　materials　consumption,　where　concrete　contributes　most　to　both　energy　consumption　(36.6%)　and　greenhouse　gas　emission　(35.9%).　Regarding　the　contribution　to　energy　consumption　and　greenhouse　gas　emission　for　building　life　cycle,　materials　production　phase　accounts　for　5.6%-18.8%　and　building　operation　phase　takes　up　80.6%-93.4%.　With　the　increase　of　EPS　insulation　thickness,　the　energy　consumption　and　greenhouse　gas　emission　increase　linearly　in　materials　production　phase,　decrease　in　building　operation　phase,　and　have　an　optimization　value　in　the　building　life　cycle　to　reach　the　minimum　when　the　heat　transfer　coefficient　(K)　is　0.3W/(m2　•　K)　equivalent　to　the　EPS　insulation　thickness　is　130mm.　Building　heating　load　reduces　with　the　increases　of　insulation　thickness,　but　the　envelope　thermal　insulation　performance　has　no　significant　influence　on　cooling　load.　©　2016　Trans　Tech　Publications,　Switzerland.