In order to research the potential of energy efficiency design of public building in depth, the large scale of store building in urban districts of Chongqing is chosen as the subject. On the basis of investigation into typical department store,an elementary model of department store has been built up. In allusion to exterior wall of department store, in respect of improving heat preservation of exterior wall, four different energy efficiency conformation design projects were made out,such as using double-layer window and adding heat insulation layer to exterior wall etc. and four energy efficiency projects with the actual design of exterior wall were compared;By analyzing the thermal and economic indexes, the most effective project of the energy efficiency design of exterior wall as to store building was found out to provide reference to the energy efficiency design of large scale of public building.