The Dianchi watershed Basin was selected as a typical watershed. Considering the differences of regional natural geography, hydrometeorology and human activities, using 1 km×1 km grid data, the detailed simulation calculation of the pollutants entering the water source of agricultural sources is carried out. The rainfall driving factors, terrain driving factors, surface runoff factor, underground storage/groundwater runoff factor and interception factor are obtained. The average comprehensive water inflow coefficients of TN and TP from agricultural sources in Dianchi Basin in 2016 are 0.447 and 0.342 respectively, and the actual water inflow loads of TN and TP from agricultural sources in 2016 are 577.39 t and 167.62 t respectively. The results show that the discharge of agricultural source pollutants and the load of influent water have significant spatial variation in Dianchi Lake Basin. 81.0% of nitrogen and 74.2% of phosphorus were concentrated in Caohai land area and the north coast of the open sea. The largest emission was in the upper reaches of Panlong River, with nitrogen and phosphorus accounting for 21.9% and 20.2% respectively. It is also found that livestock and poultry breeding account for more than 90% of the total TN and TP emissions of from agricultural sources, which should be the focus of agricultural source pollution control.