Water is an important resource for urban life and will have a certain impact on the lives of residents. Urban waterworks have a certain public welfare nature, and their economic interests have certain restrictions, coupled with some cities have different degrees of financial difficulties, so that there is a shortage of funds for waterworks, which cannot meet the needs of normal operation of enterprises.Capital is needed to invest in waterworks, to promote the long-term stable development of waterworks, and better meet the needs of market economic development. Waterworks projects have many uncertainties during construction and operation, and the uncertainty of the project cannot be fully considered by using the traditional investment decision model, which will directly affect the reliability and scientific nature of investment decisions. This study proposes an investment decision-making method for waterworks PPP projects based on fuzzy engineering economic calculation.On the basis of engineering economic fuzzy calculation, the triangular fuzzy number is used to express the uncertain economic indicators of waterworks: annual water sales and water fees, and a waterworks investment decision-making model based on fuzzy economic calculation is constructed. By analyzing the fuzzy net present value and fuzzy internal rate of return of the waterworks PPP project, the investment decision is made on the waterworks PPP project. The applicability and effectiveness of the fuzzy engineering economic method to deal with such uncertainty problems are verified through case calculation, which provides investors with multiple possibilities for project returns and helps investors reduce investment risks.