Abstract: The assessment on water quality of a reservoir in Xinyang City was made by use of the methods of indices and scoring.The results indicated that this reservoir has been polluted by phosphorus and nitrogen.The water qualty of this reservoir is not better than that of Ⅲ grade water body in envir-onmental quality standard for surface water.The reservoir is in the state of meso-to entro-phication,therefore,some protection measures should be taken.