Based on water quality data of 4 stations in the Dawen River from 2007 to 2014, this paper analyzed the inter-annual variability of 9 indicators such as dissolved oxygen, chemical oxygen demand, ammonia nitrogen etc., and evaluated water quality by a Grey Model. By the site investigation of 9 cascade reservoirs during the rich, average and dry period in 2015, the spatiotemporal variation of nitrogen and phosphorus nutrients were analyzed, nutritional level was assessed by TLI.The results show that during the period of 2007 to 2014, the organic pollution have been effectively alleviated by the emission reduction measures in the basin, the concentrations of TP have been meliorated obviously while the concentrations of TN have been aggravated integrally by the construction of cascade reservoirs. The grey comprehensive index shows that the water quality of the Dawen River is improved and the seasonal fluctuations tend to be stable. The state of eutrophication has apparent difference among cascade reservoirs because the contamination vary in degree. Part of the reservoirs have been experienced cyanobacteria and diatom blooms during rainy and dry seasons. The different flow conditions induced by different discharge in corresponding season have great influence on water quality of the reservoirs., the difference of flow condition caused by the water pollution level, damming and impoundment have a significant impact on the growth and bloom of algae in reservoirs.