With the fact that the energy saving retrofitting technology of public buildings has been continuously refurbished,the selection of technical scheme has gradually become a necessary link in the work of building energy saving. the author aims at using the analytic hierarchy process to establish the evaluation index system of the energy saving retrofitting technology of existing public buildings,simultaneously, determining the weight of each index. On that basis, the method of selecting technical scheme by using the gray correlation analysis is also provided,which will play important guiding significance in the selection of technical scheme of energy saving retrofitting of existing public buildings in northern heating areas.