| Chaohe, which can supply more than 60% with the reservoir of miyun,is the stanchion source of the reservoir of miyun.In this paper, combining the investigation of water and sand environment of Chaohe by the project"The item of continuable utilize of water resourse in the capital at the beginning of 21C",all the methods,including the improved water quality index evaluation method,fuzzy synthetic evaluation method,the water quality assessment characteristic comprehensive model and the water quality comprehensive assessment method,were applied to assess the water quality in the upper branch of Chaohe Rive from 1996 to 2000 and 2002 to 2004. After comparing the assessment result,it indicated obviously that:improved water quality index evaluation method dividing the evaluating indicators into three species considering their toxicity,difficulty of purify and value of background of source, assessed the toxicity indicators strictly and value of background or the indicators which treatmented easily undemanding ,in which way, it can assess the water quality objectively, but it was short of comprehensive. Fuzzy synthetic evaluation method blured the assess criterion,but it didn't treat the assess index differently,the result didn't coincide with the fact.Water quality assessment characteristic comprehensive model, gave the water area distinction of water quality parameters, gave the distinction of assessment reach and the water quality parameters according as, gave the water quality parameters which exceeded the criterions and the times they exceeded and it also can give information according to the specifically distinction of water quality as criterion (for example, gave water quality parameters which accorded with specifically evaluating criterion, which exceeded the evaluating criterion and the times they exceeded ), it gave lots of information but it wasn't flexible enough because it didn't treat the assess criterion differently, it regarded the indicators as the following distinction once they didn't reach the upper distinction, in this way, it was liable to assess the water quality inferior.Water quality comprehensive assessment method modeling based on tradition method, integrated both superiority of the improved water quality index evaluation method and the water quality assessment characteristic comprehensive model,with the same input, it can gave more comprehensive output than improved water quality index evaluation method given and more objective output than water quality assessment characteristic comprehensive model given, it gave water quality index, gave the general condition of water quality and give the detailed information for every water quality indicators participated in assessment. In conclusion, water quality comprehensive assessment method can reflect the water quality objectively and across-the-board.Using the water quality comprehensive assessment method to assess the water quality in the upper branch of Chaohe Rive from 1996 to 2000 and 2002 to 2004,the results are as follows: ⑴1996-2000年: The WQI value is 32.2,good; 16 N1 (pH,DO,BOD 5,VP,CN -,Hg,Cd,Pb,As,Cr +,F-)×N( 22 Cu,Zn) N( 41 COD M n) N ( 62 N H 3 -N , 0.0661,TN,1.5395) N(Ⅱ3COD Mn,0.526,N H 3-N ,3.246,TN,9.158).⑵2002-2004: The WQI value is 26.3,good; 11N ( pH,DO,N H 3 -N,VP,CN -,As,Hg,Cd,Cl- ) N (2COD Mn,Cr+).⑶Analysed the water quality trend at the points of view for different year,different water season and different position,results indicated that except for several parameters(NH3-N,TN,CODMn)exceeded the criterion, most of its water parameters were up to criterionⅡ.⑷The water quality in upriver of Chaohe River Watershed is good, there is hardly any industry pollution source, analyzing from the exceeded criterion parameter(NH3-N,TN,CODMn),the pollution source were mainly agriculture Non-point source pollution and the sewage letting from town,so the way of controlling NH3-N and TN was tightening the screws of fertilizer;meanwhile,to reduce the CODMn, destined for the given sewerage is necessary.
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