Dynamic variation of water quality in Meiliang Bay and part of west Taihu Lake has been analysed based on the data from 1991 to 1992. Principal Component Analysis is used to reveal the mutual relationships of various factors. It is shown that there exists aa obvious spatial and temporal variation in the main factors of water quality. Annual values of TP, TN, CON. Chl-a and conductivity decrease evidently from inner Meiliang Bay to the outer from north to south. TP and TN fluctuate seasonally with much higher value in winter. This is particularly true for the mouth of Liangxi River. In addition, the Chl-a has a synchronous variation with water temperature, although being lagged a little, and closely relates to TP and TN. Finally, the results from Principal Component Analysis bhow that TP. TN, SS (or SD'), water temperature and Chl-a are the most Influential factors to water quality in this area, and both suspensions and algae can contribute to the transperancy in Taihu Lake.