The Fangbian Reservoir in the Lishui district of Nanjing City was selected as the study object. The ArcGIS technology was used in the watershed subdivision of catchment area in Fangbian Reservoir, and then combined with the remote sensing technology, this study simulated the pollution intensity and spatial distribution to determine the main pollution source of inflow stream and the intensity distribution of pollution source. After that, the simulating results of ArcGIS has been validated by the actually monitored water quality. The results showed that the catchment area of inflow stream and spatial distribution of pollution source intensity can be directly reflected by the ArcGIS technology. Besides, the difference of pollution emission amount calculated between the ArcGIS simulation and the surveyed data was less than 10%.