Abstract: More than one index has to be referred when the eutrophication sensitivities are quantitatively estimated.An open quantitative index,river-lake index(RLI),which has been processed by the dimensionless and standardization method,is proposed.With RLI,the difference in hydrodynamic status in a series of zones of lakes & reservoirs can be evaluated,and a new method for the identification of eutrophication sensitivity in lakes or reservoirs can be obtained.The Three Gorges Reservoir is used as an example to show the frame form of RLI,computation steps,choice of indicators and application methods.The results of sensitivity classification for the Three Gorges Reservoir show that indicators at monthly scale adopted here are effective and reasonable for the tributaries of the Three Gorges Reservoir.