In order to improve the accuracy of river health assessment, this paper introduced the triangular fuzzy number in fuzzy theory into blind number system, and formed the extended blind number theory.Based on the theory,it set up the assessment model of river health and determined the weights of evaluation index by analytic network process theory (ANP). Based on the actual situation of Tongyu River,it carried out the river health assessment, and obtained the scores of each evaluation index and the membership degree of the different evaluation grades so as to determine the river health grade of Tongyu River which was grade three.The problem of river health mainly reflected the low rate of water quality and weak ecological system in the water function area.It is necessary to further strengthen the river restoration and management.