As the third largest freshwater lakes of China and seriously suffered by Microcystis algal bloom in recent 20 years, LakeTaihu's eutrophic status had been analyzed based on the monthly monitoring data in recent 5 years. The analysis indicated thateutrophication of Lake Taihu became more and more serious since 2000. Comparing to the mean values in recent 5 years, the waterquality variables like total nitrogen, total phosphorus, and transparency, water quality of Lake Taihu were worse than that between1991 and 2001. The summer mean of TN between 2002 and 2006 was significantly higher than that of between 1992 and 2001 (p =0.005). And the transparency mean of summer of 2002-2006 in center of Lake Taihu was only 0.34 m, which was significantly lowerthan that of 1992-2001 with a mean 0.63 m (p = 0.003). Moreover, Microcystis blooming areas in summer increased from about onefourth of the lake before 2000 to over half of the lake in 2006. Blooming season from June to October before 2000 also extend fromMay to December in 2006. Microcystis blooms occur more and more regularly in the lake. And dominant areas of submergedmacrophytes decreased quickly. The deteriorate trend of eutrophication in Lake Taihu may partly due to the abnormal dry and hotclimate in recent 2 years. However, destroy of submerged macrophytes also possibly contributed to the fast widespread of bloom.