In the intersecting system around Dianchi Lake, a mixed water purification plant was built with MBR process. To ensure that the nitrogen and phosphorus concentration of the MBR effluent met the discharge standard stably, a pilot-scale system was built on site to explore the effects of supplymentary carbon source (sodium acetate) and phosphorus removal agent (polyaluminum chloride) dosage on the enhanced removal of nitrogen and phosphorus in actual sewage, respectively. Due to perennial low concentration of influent water quality, low carbon-nitrogen ratio and carbon-phosphorus ratio of the agricultural non-point source sewage of Dianchi Lake, as well as large fluctuation of the TN and TP concentrations, the flexible use of the dual control method of external carbon source (sodium acetate) and auxiliary chemical phosphorus removal (polyaluminum chloride) or the single control method of auxiliary chemical phosphorus removal was proposed, which could save operating costs with the precondition that the nitrogen and phosphorus in the effluent could be up-to-standard discharged stably. At the same time, based on the pilot study parameters, the actual operation and regulation efficiency of the Luolong River Purification Plant was effectively improved, the optimization and adjustment time of the entire system was shortened, and the stability of effluent water quality reaching the discharge requirement in the purification plant was finally achieved. Especially the TP concentration was stably lower than the local standard requirement of 0.3 mg/L. It was estimated that the two purification plants with MBR process around Dianchi Lake could reduce TP emission up to 65.3 t per year.