By systematically analyzing the factors that influence the comprehensive benefit in the full life cycle of water-saving projects for green building,a comprehensive benefit economy model including the direct water-saving benefit,the environmental and social benefit as well as the incremental cost in the full life cycle is constructed,with the net present value as the evaluation and measurement index of comprehensive benefit.Then,the model is simulated and applied to a water-saving demonstration project for green building in West China to verify its rationality and practicality.Simulated results indicate that,in the full life cycle,the comprehensive benefit,the incremental cost and the benefit-to-cost ratio of the project reach 39.3 million yuan,9.3 million yuan and 4.2∶1,respectively,meaning that the water-saving project is of remarkable comprehensive benefit.