A large amount of high concentration of ammonia nitrogen wastewater was discharged in nitrogenous fertilizer production process, and brought bad influence to the water environment around the area. A/A/O wastewater treatment process is the domestic advanced biological denitrification process which combines the traditional activated sludge and biological nitrification process together, and the ammonia nitrogen, phosphorus, BOD, COD and SS and other pollutants in the water can be removed more effectively. Wastewater which ammonia nitrogen content is high from life and laboratory , gas water treatment, low temperature methanol wash, methanol distillation, ammonium nitrate and other devices in a nitrogenous fertilizer was treated by A/A/O process. Processing results show that this process is effective for the degradation of COD and ammonia nitrogen in wastewater, and make the pollutant indexes of wastewater meet the discharging standard.