In the later period of the design of an energy saving demonstration building in Chongqing university town, Writers use DeST-c to evaluate different forms of air-conditioning systems in terms of their effects in energy saving with the thought of "staged design". Through this method, an appropriate form of AC system as well as the way that fresh air is treated are fixed and a suitable form of cooling sources as well as its inner assortments are defined, which providing persuasive facts for the later determination of design scheme.