Water quality is affected by a number of factors, and its classification and evaluation standard are complex and fuzzy. Therefore, this paper constructed a mathematical model based on fuzzy comprehensive evaluation, select six evaluation factors such as dissolved oxygen, ammonia nitrogen, permanganate index, total nitrogen, total phosphorus, five day BOD and so on from many factors. After monitoring and comprehensive evaluation of water quality of the five typical monitoring stations including Kaifeng Bridge, Shushan Bridge, Zhangting, West Dam and Sluice of Yaojiang River, the result shows that water quality at the monitoring stations of Zhangting,West Dam and Sluice of Yao River reaches the environmental quality standard of surface water. However, water quality of other monitoring stations is not optimistic. The operation of this model is simple and reliable. The evaluation of water quality provides guidance for its rational use, so as to specially make a control project of water quality of the river.