A great amount of sediment and organic matter are involved in Taihu Lake, which deieoriates the water quality of river and lake, ence of organic pollutants on Taihu Lake water quality quantitatively, a mathematical model is proposed to simulate ihe loss processes and total amount of runoff, erosion and organic matter in typical years, in which two land use conditions of paddy field and dry land are considered.The result shows that the amounts of soil erosion and organic matter loss increase with surface drainage intensity exponentially, and organic matter content in surface runoff increases obviously during storm period.The problem must be highly thought of and some measures reducing the organic pollution should be taken in the water quality planning and management of Taihu Lake besin