Prediction of water quality is an important method of water environment management and has good guidance significance to industrial and agricultural production. Taking Chaohu Lake for example, aiming at the randomness of the changes in water quality, applying exponential smoothing method - Markov prediction, processing the data of CODMn,TP,TN of the two cross-section of the Hefei Lakeside and Chaohu Yuxikou during 2001-2010by exponential smoothing,the paper forecasted the water quality from 2011to 2013,and found out that the changes of TN as well as CODMn of the eastern half of Lake need to be paid attention to in the next few years.Which has certain guiding significance to grasp water quality change and pollution factor trend .Also found out that the forecast results of exponential smoothing method keep consistent with that of the Markov''s prediction , the combination of the two can be better applied to the prediction of water quality.