The treatment of real leachate from municipal landfill with high ammonia nitrogen (NH4(+) -N) content was investigated by using lab-scale first-stage up-flow anaerobic sludge bed (UASB)-SBR biological system. The denitritation kinetics characteristics of microbial population in the SBR reactor was also studied. Experimental results clearly showed that the average organic loading rate of UASB reactor reached 6.5 kg/(m x d), the average organic removal rate was 5.3 kg/(m3 x d). High concentrations of COD and nitrogen contained in landfill leachate were removed efficiently, average COD and NH4(+) -N of influent could be reduced from 6 537 mg x L(-1) and 2 021 mg x L(-1) to 354 mg x L(-1) and 2.8 mg x L(-1), respectively, the removal efficiencies reached 94.6% and 99.8%, respectively. Especially, above 99.2% removal efficiency of TN was obtained, and effluent TN concentration below 20 mg x L(-1), so advanced nitrogen removal was achieved in the biological system. Ammonia nitrogen was removed by high effective partial nitrification with above 90% nitrite accumulation ratio, and the denitritation kinetics characteristics of the microbial population was fit well for Monod Equation.