A quantitative methodology is proposed to identify and prioritize potential NFS pollution areas and periods within a watershed in this paper. Its procedure includes collecting original data and maps, selecting interested factors, converting the study area into a grid system, quantifying the factors, and drawing/overlaying on the microcomputers. More specifically, a Geographic Information System is employed to integrate and map such factors as rainfall, topography, plant cover, soil, control practice and chemical content in the soil. Gridmaps of every factor and pollutant generation module are finally obtained. The spatial and temporal variation of NFS pollutant generation can be identified from the gridmaps and the distribution curve of the rainfall factor. Therefore, potential NFS areas and periods are selected for control emphasis. In addition, a NFS management plan can be designed by altering controllable factors.The methodology presented was applied to the Yuqiao reservoir watershed, about 90 kilometers east of Beijing. The conclusions are as follows: (1) nonpoint source pollution almost always occurs in July and August. (2) topography and plant cover are two key factors affecting the spatial variation of NFS pollutant generation. Therefore, adjusting the existing tillage systems and implementing afforestation practices will be significant ways to manage nonpoint sources in the area. (3) the narrow belt along the Great Wall and the central part in the western watershed are potential NFS areas for the contributions of total sediment and nitrogen respectively, and the southern plain is a direct threat to the reservoir as a source of phosphorus. These areas were proposed as a priority for nonpoint source management.