The A2N process with BAF as a nitrification unit was researched aiming at the low carbon and nitrogen ratio domestic wastewater in southern China.According to the problems that effluent ammonia exceeded the standard because of the ammonia carried in surpass sludge and total phosphate couldn’t reach the discharge standard when SS of secondary settling tank was high,a secondary BAF was set up,and the total treatment effect of A2N/BAF process was studied.Results showed that the average removal rates of COD,ammonia and TP of A2N stage were 82.0%,70.9% and 90.0%,respectively.Effluent ammonia concentration of secondary settling tank exceeded 10 mg/L when influent was more than 40 mg/L.Average concentration of COD,TP,ammonia,nitrate and SS in final effluent were 35,0.35,1.06,8.01 and 7 mg/L,respectively,which had satisfied the A-level of the national standards.