Abstract: During the period from January to October of 2010, 80 water samples were collected from 10 sampling sites scattered at the main inlets and drinking water sources of the Taihu Lake for analysis of characteristics of the Spatio-temporal variation of NH₃-N, TN, TP and COD_Mn in the waters, and evaluation of water quality thereof. Results show that with the time going on, NH₃-N concentrations in these sensitive waters remained almost unchanged, TN was relatively high in April, TP in July, and COD_Mn significantly in January and March (no sample for February). Moreover, the sensitive waters located at Northwest Taihu Lake were higher than the others in concentration of NH₃-N, TN, TP and COD_Mn. Water quality evaluation shows that NH₃-N, TN, TP and COD_Mn concentrations in some sensitive waters were higher than the National Standard for Water Environmental Quality. TN and TP, in particular, 91.7% and 82.5% of samples exceeded their respective standard. Among the sampling sites, the one at the inlet of Dapu Pier was the most seriously polluted with the arithmetical mean monomial pollution index for NH₃-N, TN, TP and COD_Mn being 2.20, 14.73, 6.85 and 1.33, respectively.