Abstract: In order to solve the difficult problem of denitrification of aged Landfill leachate, single-factor test and orthogonal experiment were combined. The pH of influent, ratio of influent C/N （COD/NH₃-N） and aeration’s time were selected. Three-factor and three-level test were done to investigate their factors of ammonia-nitrogen for aged Landfill leachate with L₉ （3⁴） orthogonal table. The orthogonal experiment results showed that the pH of influent, C/N and aeration’s time were significant factors in the experiment. The order of influence on ammonia nitrogen removal rate of landfill leachate was influent pH>influent C/N>aeration’s time. The optimal conditions for denitrification in SBR treatment of aged landfill leachate were that the pH of influent was 8.0, the ratio of the influent C/N was 25, and the aeration’s time was 6 hours.