Abstract: A biological filter (anoxic filter combined with aerobic filter) was used for the removal of nitrogen in anaerobic membrane bioreactor (AnMBR) effluent. The anoxic and aerobic filter (A/O) were used for biological nitrogen removal using the residual COD_Cr in AnMBR effluent, dissolved methane and low-valence sulfur. The results demonstrated that after the anoxic filter and aerobic filter were separately acclimated for 120 d and then connected in series for further acclimation for 33 d using the real AnMBR effluent, the effluent TN of the biological filter was 17.93 mg/L with 52.7% removal rate at HRT=6 h with AnMBR effluent being the influent, which met the municipal wastewater discharge level B standard (GB 18918-2002). The effluent NH₄⁺-N of denitrification filter was 2.78 mg/L with 92.3% removal. When HRT was set to 8 h, the effluent TN of the biological filter was 14.60 mg/L with 59.0% removal, which reached the municipal wastewater discharge GB 18918-2002 level A standard. Effluent NH₄⁺-N of the biological filter was 2.22 mg/L with 93.7% removal. Meanwhile, nitrogen removal routes including residual COD_Cr heterotrophic denitrification, dissolved CH₄ heterotrophic denitrification and sulfur autotrophic denitrification were discussed and the contribution of each route was calculated by mass balance analysis. It was found that the contribution of these three nitrogen removal routes were 54.1%, 24.3% and 21.5% respectively at HRT=6 h, and 70.4%, 13.8% and 15.8% respectively at HRT=8 h. The results show that the anoxic and aerobic filter can remove the nitrogen in AnMBR effluent to meet the discharge standard with low consumption.