This study focused on the ecological demonstration rivers constructed with the guidance of the “five water treatment” in Hangzhou City. Based on the characteristics of urban rivers, an evaluation index system of ecological environmental effect was established according to the principles of comprehensive, targeted, and complete treatment, as well as data accessibility. The fuzzy cluster cyclic iteration method was used to determine the weight of each index and establish the evaluation model of ecological environmental effect of urban river comprehensive treatment projects. The ecological environmental effects of the comprehensive treatment projects for five ecological demonstration rivers in Hangzhou City were evaluated.