Water infrastructure PPP projects have a long construction period, which involves many uncertainties and complex factors, the completion time of water infrastructure PPP projects will affect the public’s attitude towards the government and the construction subject. Considering the influence of the public’s willingness to support on the construction duration of water infrastructure PPP projects, this paper analyzes the equilibrium strategy evolution process under different scenarios by establishing a three-way evolutionary game model consisting of the public, the government and the main body of water infrastructure PPP project construction, and then uses Matlab for numerical simulation analysis. The results show that there are four stable strategies for the public, the government and the project builders, which are (support, take incentives and make no extra efforts), (support, take no incentives and make extra efforts), (support, take incentives and make extra efforts) and (support, take incentives and make extra efforts). Among them, public willing to support can improve the willingness of government to take measures to encourage water infrastructure PPP projects to be completed ahead of schedule, which ultimately improves the project benefits and brings “happiness” to the public, thus increasing the government’s credibility and forming a virtuous cycle for all three parties.