Abstract：Taking Guidufu water observation section in Qingyi River as an example，a fussy comprehensive assessment model was set up to make an evaluation on water quality．It also analyzed the differences between fussy model and single index mode1．The results show that the water quality belongs to 19 according to single index model，it covers water quality of，Ⅱ ，m，and the subordinate degrees account for 0．771 6，0．178 1，0．050 3 respectively， compared with single index model，fussy model can explain the real condition of water quality．