This paper analyses the affect of the Diversion from Yangtze River to Taihu Lake on water quantity and quality of the Taihu Lake and the area around, explains that the Diversion from Yangtze River to Taihu Lake have effectively raised water supply and improved the water quality of Taihu and water environment of river network around. This paper also advances that it is necessary to strengthen water quantity and quality monitoring during the period of diversion from Yangtze River to Taihu Lake, and suggests studying how to increase a new route of diversion for extending the effect of diversion from Yangtze River to Taihu Lake.