The promotion of green building has significant contribution to the implementation of sustainable development principles. And with the enhancing awareness of environment protection, green building becomes the trend of the construction industry. While its promotion is still very difficult, the major barrier affecting the application of green strategies is the high initial cost. So the incremental costs and benefits in the life cycle of green building are identified and described by math equations in this paper. Furthermore, the evaluation indexes of incremental cost-benefit analysis, considering the social benefits and environmental benefits, are given to evaluate the economy of green project, which is of certain practical significance.