External　wall　thermal　insulation　system　protects　the　major　structure　of　building　effectively.　In　this　study,　a　student　dormitory　building　with　typical　external　wall　thermal　insulation　system　in　Beijing　was　chosen　as　the　research　object　and　the　energy　consumption　analysis　was　conducted　to　identify　the　optimal　external　thermal　insulation　system　during　the　whole　life　cycle.　The　results　show:　for　brick-concrete　buildings,　the　consumption　of　clay　brick,　reinforced　concrete　and　cement　mortar　account　for　more　than　95%　of　the　total　materials　consumption,　where　reinforced　concrete　contributes　most　to　energy　consumption.　The　external　insulation　system　with　similar　heat　transfer　coefficient　but　consist　of　different　insulation　materials　mainly　affects　energy　consumption　in　materials　production　phase　(the　difference　of　building　production　energy　consumption　is　about　7.2%),　while　has　no　significant　effect　in　building　operation　phase　and　whole　life　cycle.　With　the　increase　of　heat　transfer　coefficient,　the　energy　consumption　decreases　in　materials　production　phase,　accounting　for　16.3%-21.9%　of　the　life　cycle　energy　consumption,　increases　in　building　operation　phase,　accounting　for　78.1%-83.7%,　and　can　be　neglected　in　the　disposal　phase.　And　there　exists　an　optimization　value　in　building　whole　life　cycle,　at　which　the　minimum　value　of　the　energy　consumption　reaches,　when　the　heat　transfer　coefficient　is　0.3W　/(m2　•　K),　equivalent　to　127mm　EPS　insulation　thickness　or　151mm　rock　wool　insulation　thickness.　©　2017　Trans　Tech　Publications,　Switzerland.