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A universal power index formula based on a power function of weighted sums is proposed for evaluation of the eutrophication level of lakes,with parameters optimized by Particle Swarm Optimization.Then,a comprehensive impact factor is constructed by integrating multiple factors closely related to lake eutrophication,including the discharge amount of industrial and domestic waste water,load ratio of agricultural non-point source organic pollution,standard discharge rate of industrial waste water,and domestic waste water treatment rate,etc.On such basis,the paper proposes a comprehensive formulae with upward semi -(Γ) distribution for eutrophication prediction,a special case of which can also be suited for single index prediction.In the formula the comprehensive impact factor serves as the independent variable.Particle Swarm Optimization (PSO) is used to optimize the parameters in the prediction formula.By applying the prediction formula to the practical eutrophication tendency of Taihu Lake in the coming years (2005～2035),the results of this prediction,which correspond to the real conditions,show that Taihu lake will gradually transfer from the current eutrophication state to "heavy" eutrophication state in less than 10 years if no control measures are adopted.Therefore,the paper makes some suggestions on harnessing the serious eutrophication state of Taihu lake.