Water diversion project is an important means to solve the uneven spatial distribution of water resources and an important part of infrastructure. However, there are many uncertainties in the operation of water diversion project. The traditional investment decision-making model cannot fully consider the uncertainty of the project, which directly affects the reliability and scientific of investment decision-making. In order to solve this problem, a method of investment decision-making of water diversion project based on fuzzy economic calculation is proposed and the uncertainty of the project is fully described by fuzzy number. The applicability and effectiveness of the model are verified through the calculation of case study, which improves the scientific and accuracy of decision-making and it has a high guiding value for project risk aversion.