The quantitative analysis of pollution source is the important basis for the formulation of pollutants reduction plan and control measures preference. The paper chose GWLF（Generalized Watershed Loading Functions）model to improve rural life and livestock module and simulate monthly runoff and total nitrogen (TN) load in Liuhe River watershed.It analyzed the contribution rate and seasonal variation of pollution source based on model result. Except individual flood peak values were underestimated,the simulation effects of monthly runoff and TN load simulated by model were better. The result indicated that there are seasonal significant difference of the contribution ratio from TN pollution source. Overall, the contribution rate of non point source pollution in flood season is higher than that in non flood season; However, the contribution rate of point source pollution in flood season is much higher than that in non flood season. The point source pollution is the major pollution source in non flood season. In order to efficiently reduce and control nitrogen pollution in Liuhe River watershed,it is necessary to fully consider the difference of pollution source constitution between flood and non flood season in the formulation of pollutants reduction plan and control measures preference.