Abstract: In order to study the influence of water diversion from Yangtze River to Taihu Lake, water samples were collected from Taihu Lake subzones, and the activity of alkaline phosphatase was determ ined together with water quality parameters.The study is focuses attention on the variation of the maximum reaction rate in alkaline phosphatase activity (v_max) and the Michaelis-Menten constant (Km_m) due to the water transferring activity Results show that differences exist in the tem poral and spatial distribution of both v_max and Km_m of Taihu Lake subzones.The concentration of blue-green algae in Taihu Lake subzones is diluted as a result of water diversion, which inhibits the maxmium reaction rate in alkaline phosphatase activity.A quadratic relationship (p=0 007) bewteen Km_m and accumulated water into Taihu Lake is found for the subzones of Gonghu Bay, Western Estuary, and Taihu Lake Centre.The alkaline phosphatase (v_max/Km_m) increases with the increase of the total phosphorus concentration in the subzones of Meiliang Bay, Zhushan Bay, Gonghu Bay, and Western Estuary However, v_max/Km_m decreases with the increase of the bioavailable phosphorus concentration in the subzones of Zhushan Bay, Gonghu Bay, grass type area, Western Estuary, and Taihu Lake Centre.The v_max/Km_m is enhanced when the concentration of chlorophylla increases except for grass-type area.