The deterioration of water resources and surface water eutrophication threaten the health of the ecological environment seriously. Nitrogen (N) pollution from agricultural activities is an important source of water pollution. In this study, the Jurong Reservoir agricultural watershed was taken as the research object, and the local applicability of the SWAT model for N pollution was validated based on field monitoring data. In addition, the spatial and temporal distribution characteristics of N load and key pollution sources were analyzed. During the monitoring period, the annual N load showed an "M" type fluctuation trend, with a high N load occurred in the flood season from June to September, which accounted for more than 84% of the total N load of the whole year. Moreover, the spatial distribution of nitrate nitrogen (NO₃^--N) and total nitrogen(TN) load showed a trend of "local concentration, adjacent to water body", mainly concentrated in the area with a high proportion of farmland. Farmland fertilizer is the main source of TN load in this watershed, contributing to 49.60% of total N load and the average annual storage capacity of NO₃^--N and TN was 9.98 t and 27.22 t, respectively. Our results can serve as a theoretical basis for the control of N pollution at the watershed scale.