Based on the monthly data of chlorophyll-a, nitrogen forms, phosphorus forms and water depth observed by the TaihuLake Ecosystem Research Station under Chinese Academy of Sciences from 2005 to 2009, and the daily water level data from theDapu Station, the daily water quantity of the Taihu Lake from 2005 to 2009 was estimated, and the Tyson polygon method wasused to estimate the monthly variation of total nitrogen (TN), total phosphorus (TP), total dissolved nitrogen (TDN), total dissolvedphosphorus (TDP), nitrate nitrogen (NO3), ammonium nitrogen (NH4), nitrite nitrogen (NO2), reactive phosphorus(PO4), total particulatenitrogen (TPN), total particulate phosphorus (TPP), planktonic algae chlorophyll-a (Chl-a) in the Taihu Lake. The results show that:(1) The average volumes of TN, TDN, NO2, NO3, NH4, TP, TDP, PO4, TPN, TPP, Chl -a are respectively 1.36×104t,, 1.02 ×104t,0.02×104t, 0.37×104t, 0.25×104t, 514.34t, 147.30t, 51.44t, 0.34 ×104t, 367.04t, 7.92t in the Taihu Lake during 2005 -2009. Themonthly and annual change are violent. The relative amplitude are respectively 106%, 142%, 657%, 252%, 233%, 95%, 196%,276%, 236%, 131%, 276%. (2) Since the Wuxi water crisis in June 2007 untill the end of 2009, the decline trend of variousnitrogen forms and total phosphorus in the Taihu Lake is not obvious, and the volume of dissolved phosphorus and reaction activityof phosphate increased. This study shows that as for large lakes with great change amplitude of water quantity, the volume of lakenutrient is a valuable indicator in the assessment of nutrient pollution. In the view of pollution control, it is not perfect only toevaluate the concentration, and it is necessary to pay attention to nutrient volume changes.