Abstract: According to the distribution and pollution characteristics of aquaculture wastewater from inland fresh ponds, the multistage combined treatment system of “sedimentation pond+filter dam+aeration pond+filter dam+ecological pond” (referred to as “three ponds and two dams”) was adopted to purify the aquaculture wastewater. The removal effect of the combined process on the main pollutant indexes of wastewater and the removal contribution rate of each unit along the way of three demonstration sites corresponding to low pollution, medium pollution and high pollution types were investigated. The project construction investment and operation cost were analyzed. The results showed that the average removal rates of TSS, COD_Mn, TN, TP and NH₄⁺-N in the three demonstration sites ranged from 48.1% to 60.7%, 50.4% to 60.7%, 52.5% to 59.2%, 64.2% to 71.5% and 72.1% to 80.5%, respectively. Water quality at the outlets was improved obviously and met the standard of Requirement for Water Discharge from Freshwater Aquaculture Pond (SC/T 9101-2007) stably. The treatment effects of combined system in summer were the best, followed by spring and autumn. Even in winter, the system could still run normally and stably to ensure that the water quality reach the standard. Sedimentation pond had the best purifying effects on TSS with the removal rate of 21.3%. Aeration pond had the largest contribution to COD_Mn and NH₄⁺-N with the removal rates of 18.7% and 28.7%, respectively. Ecological pond had the largest contribution to TN and TP removal rates with 16.3% and 28.8%, respectively. The filter dam had good removal effect on all water quality indexes, and the removal range was 7.5% to 11.8%. The construction cost of the aquaculture pond tail water projects were 13 700, 27 750 and 13 040 yuan/hm² for the three demonstration sites. The annual operating and maintenance costs allocating to the ponds every year were 3 250, 3 870 and 4 000 yuan/hm², respectively.