Abstract: The average value of mineralization degree of water in river system of Dongting Lake is 160 mg/L(the highest is 260mg/L,the lowest is less than 50mg/L).The mineralization degree in rivers of this system presents a decreasing trend from the northwest and southwest of the system and hills north to the Nanling Mountain,to the northeast outlet of Dongting Lake,due to the differences in climate and hydrology,as well as the differences in association of geology,geomorphology and soil.The ion flow in rivers and lakes of this system has an obvious seasonal change. The river system is a strong chemical denudation region.The main factors to influence chemical denudation are precipitation,runoff and soluble and non-soluble substances,and geomorphology and vegetation as well.