Anammox-based nitrogen removal can advance sustainable wastewater treatment, especially for the mainstream wastewater treatment. Two lab-scale Anammox biofilm reactors fed with influent ammonium concentrations of 110 mg/L (Anammox-H) and 50 mg/L (Anammox-L) were operated, and nitrogen removal and mechanisms of quorum sensing (QS)/quorum quenching (QQ) were examined. The achieved nitrogen removal rates were 0.65 g N/L.d in Anammox-H and 0.25 g N/L.d in Anammox-L. Candidatus Kuenenia was dominant in both reactors. Higher contents of tight extracellular polymeric substance and hydrophobic amino acid confirmed that dense Anammox biofilm developed in Anammox-H. N-hexanoyl-L-homoserine lactone and N-octanoyl-L-homoserine lactone were detected in Anammox-H and Anammox-L. High concentrations of acyl-homoserine lactones (AHLs) in water and biomass phases of Anammox-H were consistent with that more active QS processes existed in Anammox-H. Functional genes including hao, pmoA-amoC, nirK and narGZHY were detected and harbored by Candidatus Kuenenia stuttgartiensis, Nitrosomonas europaea and Lautropia sp. SCN 69-89. These organisms not only involved in nitrogen metabolism, but also in pyruvate, fatty acid and S-Adenosy-L-methionine synthesis (important for AHLs). Influent ammonium concentrations affected the balance between QQ and QS activities, resulting in different Anammox activity and biofilm morphology. This study advanced the Anammox application for low-strength wastewater, especially from the aspect of QQ and QS balance.