SWAT model and measured data were used to simulate the Non-Point Source (NPS) N and P pollution from 2001 to 2010 in Lake Nansi watershed.The spatial distribution of the pollution was analyzed,and the contribution of all the rivers in watersheds to the pollution of Lake Nansi were calculated.The key areas with serious pollution were distinguished.The results indicated that: (1) typical watersheds were simulated with SWAT model,and then the derived models were used to simulate the Lake Nansi watershed.This method can not only improve efficiency,but also with higher simulation accuracy.The simulation results in the east of the lake were better than those in the west part of the lake,which indicated that SWAT model was suitable for the hilly areas.(2) The NPS pollution was serious in Lake Nansi watershed.The nitrogen loading exceeded the criteria in almost all regions, and the phosphorus loading exceeded the criteria in more than 40% of the region.The NPS pollution was more serious in east than that in west of the lake.The Guangfu River watershed was the major contributor to the NPS pollution in Lake Nansi watershed.(3) The soluble nitrogen,flowed into the lake through streams,is the main form of loading in Lake Nansi watershed.While,the P loading in Lake Nansi watershed was mainly in the form of adsorption,which ran into river with sediment.