Large-scale public building has high energy consumption and has great potential in saving it. It is necessary to do research on the calculation of energy consumption and raise some methods to save energy of large-scale public building. Basing on the theory of whole life cycle, the energy consumption of large-scale public building was analysed and the whole life cycle energy saving system was set up. What's more, it emphasized the importance of energy saving design at the stage of planning and design. Meanwhile, the paper not only analysed the whole life cycle energy saving contents and calculation formulas of large-scale public building by taking advantage of LCEA model, but also proposed some corresponding measures to save energy.