This research was conducted in a typical agricultural small watershed in the western Sichuan Basin. The nitrogen (NH₄⁺-N, NO₃^--N, TN) concentration and pH in Xihe river were continuously monitored from March 2015 to February 2016. Using different techniques, such as remote-sensing interpretation, geographic information systems, and correlation analysis, the relationship between nitrogen concentration and pH in the river with surrounding land use typed area was explored. Results showed that river nitrogen concentration was higher in the winter (2.063mg/L) than in spring and autumn (1.536mg/L; 1.432mg/L), followed by summer (1.085mg/L). Concurrently, the monthly average concentration of NO₃^--N (0.891mg/L) was significantly higher than that of NH₄⁺-N (0.425mg/L) (P<0.01), and NO₃^--N was remarkably affected by typical land use types. As the buffer zone radius increased, the correlation of cultivated land, urban-rural construction land, and water area with NO₃^--N and TN concentrations gradually decreased. In the 250m buffer zone, the area of urban-rural construction land was significantly positively correlated with NO₃^--N concentration (P<0.05), and the transportation land was increasingly correlated with all nitrogen components. In the 750m buffer zone, the area of transportation land was significantly positively correlated with NO₃^--N and TN concentrations (P<0.01). Urban-rural construction land and transportation land may be the "source" of river NO₃^--N.