Under the background of accelerating the construction of green urbanization, the PPP project of water environment treatment has a positive role in stabilizing investment, making up for weakness and benefiting people's livelihood. Owing to the problem of high risk of social capital induced by strong quasi-public welfare of PPP projects, difficult integration of treat techniques, complex assessment of treat effect and difficult coordination of water environment treatment, five first-class and 16 second-class indices of financing, finance, project technology and management, government regulation and environment are summarized based on the literature reading method. The risk of social capital is analyzed by the fuzzy-DEMATEL method. The key factors in PPP projects of water environment treatment are determined by the MATLAB software, and the result chart of risk factors is established. Finally, some suggestions are put forward, including innovating the payment mechanism of project return, reforming the fiscal and taxation system of the government, clarifying the principle of handling the change of assessment standards, establishing the restraint and punishment mechanism, and enhancing the credibility of the government so as to reduce the project risk and provide some reference for promoting the rapid development of PPP projects of water environment treatment in China.