Abstract: Based on catchment delineation, land use, soil hydrologic group classification and precipitation data processed by 3S (GIS, RS and GPS) techniques, a nonpoint source pollution model for the index of total nitrogen (TN) of Daya Bay was built used the LongTerm Hydrologic Impact and Non Point Source Pollutant model (LTHIA). The model rationality was verified by comparing the modeling results of runoff and load and the results of different methods. It showes that the annual nonpoint source TN load of Daya Bay was 2 559 tons. The farmland，builtup area and orchard were the main types of land use for TN loss due to the high load and loss intensity. Among 11 towns, Renshan town and Pinghai town contributed more than 50.0% of TN load and occupied 77.7% of critical source areas. Thus more attention should be paid to these towns in the work of nonpoint source pollution control. The quantification of load contribution and the identification of critical source area will help local decision makers to administrate the nonpoint source nitrogen pollution effectively and efficiently.