In consideration of the climatic characteristics of different climatic zones, the annual energy consumption of existing buildings before and after reconstruction in hot summer and warm winter regions of South China and cold regions of North China is analyzed in this paper using DOE-2 dynamic cold and heat load simulation software. For cold regions of North China, the annual comprehensive energy saving benefits of existing buildings reconstruction in summer and winter should be analyzed, and the cost savings in the initial investment for heat resource and electricity construction should also be included at the same time. While for hot summer and warm winter regions of South China, the building energy saving should focus on new buildings. The building energy saving reconstruction and the feasibility in the two regions is also compared and analyzed. (C) 2012 Elsevier B.V. All rights reserved.