The paper analyzed the variation situation of water quality indicators of eutrophication in Taihu lake from 1980 to 2011.By use of the evaluation result of water quality eutrophication it analyzed the variation feature of nutrition level in different lake areas from 2002 to 2011.The results indicate that the eutrophication indicators rise generally. Although TN and TP have decreased since 1996, they are still on a relative high level. The maximum of NH+4-N and Chl-a appeared in 2006. TN and NH+4-N share a similar monthly variation character, but the extreme value of NH+4-N turn up one month earlier than those of TN. CODMn and Chl-a presents the unimodal character of monthly variation,but that of TP presents double-peaked. Improvement of water quality in west zone and Wuli lake is obvious, but the improvement in Meiliang lake, Zhushan Lake and south zone is not significant.The water quality in east beach zone and Dongtaihu lake exhibits a downtrend. There are also obvious variation characters of the monthly occurrence frequency in the subzones.