[Objective] The objective of this study is to explore the distribution characteristics of the output risk of non-point source pollutants nitrogen(N) and phosphorus(P) under different conditions of sub basin, slope grade and geographical demarcation(counties), and to provide scientific basics for administer plan and control countermeasure of different risk areas of Nansihu Lake Basin.[Methods] Based on digital elevation model(DEM) data, the Nansihu Lake Basin DEM was extracted and slope grade was extracted using ArcGIS software. Then applying hydrologic analysis function, we extracted the drainage and river figures and delimited the drainage basin. Combined with the land use map of Nansihu Lake Basin in 2013, the space changes of N, P pollution under different land cover and slope were analyzed using the output risk model.[Results] The average risk probability of N reached 51.67%. The average risk probability of P reached 9.14%. The output risk of non-point source pollution in the east of lake was less than that in the west. With the increase of slope, the high risk area reduced, but the low risk area increased. In terms of geographical demarcation, Jining City was determined as less risk area of N, other counties had higher risk. The risk of P was less for all counties.[Conclusion] Nitrogen is the main basin non-point source pollutants. The output risk value of non-point source pollution has close relationship with land cover and slope.