The changes of water quality at an upstream river of Taihu Lake near Linzhuang Port which located in Dapu town, Yixing city were investigated from October 2004 to September 2005. The results showed that the concentration of TN was worse than class V water quality all over the year. The other indices were near class II to class IV. The eutrophication of water was mainly represented as the exceeding of TN. Except the concentration of TN and TP, the other water quality indices were worse in growth season than that in non-growth season. The changes of BOD5, CODMn, Chla were mostly affected by temperature. Temperature was the active factor for BOD5 and COD. Precipitation only had positive correlation with the concentration of TP. It showed that TP was influenced little by ecological process of river ecosystem than others such as TN.