The drainage process during aquaculture pond cleaning would cause non negligible pollution of surrounding water environment, but there haven't been sufficient research on the characteristics of pollutant discharges and the impact degrees of this process. To effectively mitigate the environmental pollution from the drainage of pond cleaning process and promote the green development of aquaculture industry, in this study, we selected a typical intensive fish aquaculture area as the study object. Through high frequency sampling, we analyzed the changes of suspended matters, organic matters and nutrients concentrations in the tailwater of mixed fishponds to understand the discharge characteristics of pollutants. The changes of water quality in different sections of the receiving water were analyzed as well. According to our results, the concentrations of total suspended solids concentration (TSS), COD_Mn, total phosphorus (TP), total nitrogen (TN) and ammonia nitrogen (NH₃-N) all exhibited an increasing trend with the drainage and increased rapidly at the end of the drainage event. The concentration of phosphate (PO^3-₄-P) increased rapidly only at the end of the drainage event, while the concentration of nitrate nitrogen (NO₃^--N) decreased continuously during the whole drainage event. According to the secondary standard of "Freshwater Pond Culture Water Discharge Requirements", the exceedance multiples of TN, TP and TSS at the end of discharge reached 4.70, 6.66 and 206.90, respectively. After the tailwater flow discharged into the external river at a ratio of about 1/200 to the river volume, within 400 m from the outlet, only TSS, COD_Mn, TN and NH₃-N would significantly affect the river water quality, and the influencing distance exhibited a trend of TN>TSS=NH₃-N>COD_Mn. Therefore, prohibiting direct discharge of aquaculture tailwater into the nearby river without treatment, especially the tailwater of the last 20-30 cm water depth of the pond, can effectively limit the output loads of the concentrated pollutants in aquaculture tailwater.