Abstract: Based on understanding and analysis of the migration mechanism of non-point source pollutants, the method of combining watershed unit and river network analysis was used to explore the impact of spatial locations on the inflow ability of non-point source pollutants into the lake. The distance weight was used to represent the impact degree of the polluting sources in the watershed on the lake water environment. With Zhushan Bay as case study, a river network model was constructed by ArcGIS, which was used for watershed unit division and origination-destination (OD) cost matrix analysis. The distance weight of non-point source pollution in watershed was thus calculated, and then tested by pollution contribution coefficients. The results show that the inflow ability of the pollutants into the lake is affected by the polluting source’s location or the migration route distance of the pollutants. The distribution of the same distance weight unit conforms to watershed unit, and the inflow coefficients of TN and TP into the lake are positively associated with the distance weight.