Abstract: The role of spatiotemporal distribution of agricultural non-point source pollutants, including total nitrogen (TN), total phosphorus (TP) and Atrazine in the Little Arkansas River watershed in the United States were monitored and analyzed, in order to provide guidance for the analytical investigation and further treatment of similar pollutants at a watershed scale in our country. The three sampling sites along the main stream of the river were located in upstream, midstream, and the outflow of the watershed. The rainfall and flow rates were monitored in real time and the water quality parameters of TN, TP and Atrazine concentrations were periodically detected. The results showed that: the factors most influencing all of the water quality parameters were the crop plant area in the watershed and the rainfall intensity and timing. The peak concentrations of both TN and TP were obtained in the lower portion of the watershed, and the loss amount of TN and TP in rainy year was about twice as much as that in drought year. Whereas, the most Atrazine lost occurs in the midstream portion of the watershed. During the period of observation, there was a large amount of TN and TP lost throughout the watershed and the Atrazine concentration was above the critical value of 3 μg/L, which should be paid enough attentions. It was suggested that the best management practices (BMPs) should be implemented to reduce the agricultural non-point source pollutants.