Abstract: As a spare water head site of domestic water resources for Harbin,The water quality of Xiquanyan Reservoir is closely related to water security of millions of citizens.The upstream of Ashi River basin is the main sub basin of Xiquanyan reservoir and its water quality directly affect water quality of the reservoir.The water quality in upper reaches of Ashi River was assessed by the methods of single factor pollution index and grey connecting evaluation method based on the monitored physical and chemical index of the water quality in September 2010.The results showed that the water quality in all sampling points was in GradeⅠexcept for R8（Grade Ⅱ）.Grey evaluation method was found superior to single-factor method for the evaluation,which was closer to the actual situation of upper Ash River basin.Single-factor pollution index only revealed pollution degree of certain pollutant instead of the whole water body.Meanwhile,the Gray evaluation method will take advantage of environmental monitoring data and comprehensively analyzed the water pollution better.

Key words: upriver sections of Ashi river, water quality, Grey relational evaluation, quality assessment