Based on the monitored data, the trend of water quality and eutrophication extent at each monitoring site of Dongchang Lake during 2004-2011 were analyzed by single factor index, Nemerow index method and trophic state index method. The results showed that the single factor index of hydrogen ion concentration(pH) and dissolved oxygen(DO) displayed a fluctuating upward trend, and the water quality was conformed with the water quality standard of Class IV. The single factor index of chemical oxygen demand(COD_Cr) and total nitrogen(TN) displayed a fluctuating declining trend; total phosphorus(TP) displayed a fluctuating upward trend, and the three single factor indices were higher. Total nitrogen(TN) had the greatest impact on water quality. Nemerow index of Nanguan, Xiguan Bridge showed upward trends, suggesting that the water quality got worse. Nemerow index of Beiguan, Dongguan Bridge showed a declining trend, demonstrating the water quality became better. Eutrophication of each monitoring site was in light-middle eutropher level during 2004-2010, which reached mesotropher level up to 2011. The eutrophication levels of Dongguan and Beiguan Bridge were higher than those of Xiguan and Nanguan Bridge.