Considering the defect in the conventional methods for river health evaluation, this paper presents a new method for evaluation based on triangular fuzzy number expected values. At first, we built the grading indicator system of evaluation based on triangular fuzzy numbers. And then, we confirmed the ideal points of all grading using the triangular fuzzy number expected values formula, and build standard decision matrix based on the ideal point and the index value of evaluation object. After that, we determined the weight of each indicator dynamically using entropy coupling method based on AHP-PPC. At last, we calculated the chi-square distance between evaluation object and ideal points, which determined the grade of evaluation object by cluster analysis. The algorithm designing and data computing is achieved easily using computer in the method. It avoids excessive interference from human factors, as can gain experience from specialist. In this way, the result is on the verge of true value. We proved the new method reasonable and handy when applied to evaluate the health of Pengxi River in Yunyang County, Chongqing.