According to the occurrcnce of the typhoon (No. 9711), the effects on the water level of Taihu Lake has been evaluated. The results show that this strong windy process had exerted a remarkable effect on the lake level in the east and the west of lake. In eastern lake，the water level decreased dramatically, i. e. the drop of water stand ca. 0. 66-0. 93m. However? the water level increased in western lake ca. 0.67-1-22 m. Moreover, the difference of lake level between the east and west is about 1. 03-1. 42 m，and the amplitude of changes is about 1.29-1. 62.