Life cycle assessment (LCA) has become an international recognized method to estimate the environmental impacts of a building during its life. A building’s environmental impacts can be divided into two parts－impacts in the service stage and impacts in other stages of its life cycle. Other stages comprise material acquisition stage, constructing stage and final disposal stage. In life cycle except service stage, the LCA analysis was made on a timber structure teaching building using Athena software Eco-calculator. Then the teaching building is assumed to be redesigned adopting the structure of RC-frame and steel frame respectively. And the LCA analysis was made on the two assumed buildings too. By comparing the results, the conclusion can be drawn that timber buildings have lower environmental impact indexes compared with that of RC-frame and about the same with that of steel structure. The aboard usage of the timber structure instead of RC-frame structure can result in good environment performance. In service stage, if a sensible thermal insulation scheme is also considered, a great amount of energy will be saved, and the environmental impact of a building can be made minimum.