The paper introduced a method of basin model about total nitrogen source apportionment faced on administration.Based on generalized watershed loaded function(GWLF), combined with net anthropogenic nitrogen inputs(NANI) and geographic information system(GIS), it implemented user-defined area(administrative) simulation through linking up the watershed boundary partition and administrative region. This method has a good application in Xin'anjiang basin.The results show that Xiuning County, Tunxi District, She County account for 15.5%∶41.4%∶43.1% in total nitrogen pollution to the Jiekou state-controlled section.The different districts show administrative regional characteristics.The method can achieve analyzing different administrative regions' total nitrogen source apportmention and providing effective decision-supported information for the watershed partition management of water environment.