Identifying the main pollutants of non-point source pollution within the scope of small watersheds, carrying out load estimation, and probing its mechanism and characteristics can provide a basis for water quality control and management. The nutrient loss characteristics, load, and reduction rate of nutrients under different land use types were analyzed through the runoff plot monitoring experiment, and the non-point source pollution load in the watershed was further calculated. Results showed that the loss of nutrients in each runoff plot was farmland>grassland>orchard in each runoff plot. Under the same slope, the loss of nutrient performance was maize>sweet potato>grassland>orchard. Taking S12 as the control group, the best reduction rate was orchard>grassland >sweet potato>maize>peanut. In runoff plot, the pollutant concentration under a single rainfall increased first and then decreased with the rainfall time. The pollutant concentrations sharply increased with the increase in flow, then gradually decreased, and finally stabilized at the outlet of the small watershed under a single rainfall. At this time, the shallow nutrients on the surface were easy to scour into the river, resulting in the sharp rise of pollutants in the river. In 2020, the losses of ammonia nitrogen (NH3-N), nitrate nitrogen (NO3-N), total nitrogen (TN), orthophosphate (SRP), and total phosphorus (TP) in the basin were 41.77, 296.93, 494.51, 33.87, and 44.03 kg/km2, respectively. TN and TP were the primary nutrients in this area. The research results can provide a reference for the study of non-point source pollution in similar areas.