The aim of this work was to evaluate the influence of FMA biofilm on nutrient removal through the filtration membrane air-cathode (FMA) replacement test. The result showed that the biofilm accounted for only 29.9% of the COD removal, while 82.9% of the TN removal can be due to the contribution of the FMA biofilm. The microbial community analysis showed that most of the primary genus in the FMA biofilm were TN removal related bacteria. This quantitative determination of the FMA biofilm influence on COD and TN removal would promote the further optimization of the MFC reactor with FMA for higher wastewater treatment efficiency.