A post-evaluation system for the post evaluation system of water conservancy parks based on the six main functions of water conservancy parks, that is, preservation of water conservancy projects, protection of water resources, improvement of water environment, rehabilitation of water ecology, promotion of water culture and development of water economy, which has integrated logic, independent statistics, strong guiding significance and striking application ability. Then the theory of the lattice order decision-making is introduced, and the grey lattice order method is employed to reveal the relative advantages and disadvantages among water conservancy parks. For satisfactory post-evaluation of water conservancy parks, the proposed method is also served as a try to explore new post-evaluation means to their construction. By taking two national water conservancy parks A and B in Nanjing City as case studies, the post-evaluation results show that their major functional constructions are largely efficient. Compared with those in 2014, their major functions in 2016 are improved to certain extent.