The water quality at present of Danjiangkou reservoir in water source area of Middle Route Project of South to North Water Transfer is presented and influence factors and the existing problems are analyzed.The results demonstrate that the water quality at present of Danjiangkou reservoir is qualified and meets water quality requirement as water source,but water quality pollution control surrounding the reservoir and in the upstream area falls behind severely,being a hidden trouble of water quality of the reservoir.The quality control and treatment of water shoulld be strengthened with powerfull measures to protect water quality in the reservoir to safeguard clear water flowing toward north.The pollution in Danjiangkou reservoir area is non-point pollution and water body pollution in the reservoir bays.In the light of pollution situation at present,the countermeasures are suggested.