Abstract: To investigate the long-term performance of organic and nitrogen removal from municipal landfill with high ammonia nitrogen (NH₄⁺-N), which was investigated by using a lab-scale up-flow anaerobic sludge bed (UASB)-anoxic/oxic (A/O) biological system. Experimental results clearly show that the simultaneous denitrification and methanogenesis are obtained in the UASB reactor, and almost 100% of denitrification is obtained. When the feed ρ(COD) is ranged from 1 237 mg/L to 13 813 mg/L, with an average value of (5 640±2 567) mg/L, the effluent ρ(COD) in the biological system fluctuates in the range of 280 mg/L and 1 257 mg/L, with an average value of (546±285) mg/L. When the influent ammonia nitrogen (NH₄⁺-N) varies widely from 148 mg/L to 2 414 mg/L, the effluent NH₄⁺-N is always below 50 mg/L. Moreover, the A/O reactor overcomes the disadvantageous effect of the temperature on the biological reaction and the efficient nitrification and dentrification is maintained in the A/O reactor. Even though the temperature drops below 15℃, the nitrogen removal efficiency in the A/O reactor reaches above 90%.