In this study, a pilot-scale system was built on site to explore the relationship between the dosage of exogenous carbon (sodium acetate) and phosphorus removal agent (polyaluminum chloride) on the enhanced removal of nitrogen and phosphorus in actual sewage. It is proposed that the perennial influent water quality concentration, carbon-nitrogen ratio and carbon-phosphorus ratio of the agricultural non-point source sewage of Dianchi Lake are low, and the TN and TP concentrations fluctuate greatly. Flexible use of the dual control method of external carbon source (sodium acetate) and auxiliary chemical phosphorus removal (PAC) or the single control method of auxiliary chemical phosphorus removal can save operating costs on the premise that the nitrogen and phosphorus in the effluent can be stabilized.At the same time, based on the pilot study parameters, it effectively improved the actual operation and control efficiency of the Luolong River Purification Plant, shortened the optimization and adjustment time of the entire system, and finally achieved the stability of the purification plant's various effluent water quality standards, especially the stable TP concentration. It is lower than the local standard requirement of 0.3mg/L.The methods and results reported in this article can provide a reference for the production practice of strengthening the regulation of nitrogen and phosphorus removal processes in similar domestic sewage plants.