The performance of nitritation were investigated in continuous flow MBR fed with old landfill leachate, the inhibition of substrate, product and toxicant on nitritation process and the inhibition kinetics were analyzed. The results show that:the nitritation process was started up in MBR which controlled the NH₄⁺-N concentration of inflow was (280±20) mg/L, the DO was 0.5~1.0 mg/L, pH was 7.8~8.2 and temperature was (30±1)℃; and at 32d, the nitrite accumulation rate was 84.27%. Influent load was increase gradually and improved the DO to 2~3 mg/L in the next period, nitritation process was realized gradually in MBR system which the inflow was the old landfill leachate completely, the ρ (NO₂^--N) of effluent from system was 889 mg/L and the nitrite accumulation rate was 97.23% at 112d. The inhibition experiments of substrate, product and toxicant showed that, the inhibition of toxicant surpass substrate and product, when the concentration of toxicant (calculated by COD) was 1600.2 mg/L, the ammonia oxidation rate declined by 22.15%, and if inhibition factor was FA only in corresponding conditions, ammonia oxidation rate decreased by 4.74%~6.49%, and if inhibition factor was FNA only in corresponding conditions, ammonia oxidation rate decreased by 14.46%~15.86%. Haldane model, Aiba model and the revised toxicant inhibiting model were adopted for nonlinear fitting on the experimental data respectively, the correlation coefficient R² were 0.9821, 0.9961 and 0.9924 respectively, and the inhibition kinetics models of substrate, product and toxicant were obtained.