Based on the addition of iron-based bio-carrier, the function of septic tank was strengthened by the related physicochemical and biochemical reactions, achieving the advanced treatment of fecal sewage. The effect of dissolved oxygen (DO) and carbon to nitrogen ratio (C/N) on the removal of pollutants in the fecal sewage was investigated. Under the obtained optimal operation condition, the transformation mechanism of nitrogen was further explored. The results showed that average NH₄⁺-N, TN, COD and TP removals of 90.74%, 85.81%, 92.65% and 95.78% were achieved, respectively, at the influent C/N ratio of 7.3~8.4 and optimal DO of 2.3~2.7mg/L in the aerobic iron-based bio-carriers pool. When reducing the influent C/N ratio from 3.3~4.2, the system could still maintain average NH₄⁺-N, TN, COD and TP removals of 81.16%, 76.62%, 93.87%and 94.75%, respectively. Mechanism analysis indicated that the addition of iron-based bio-carriers markedly strengthened TN removal, COD degradation and TP immobilizationof thedeveloped septic tank. Analysis on nitrogen transformation confirmed that denitrification was enhanced by the internal electrolysis and denitrifying bacteria coupled denitrifying process, which reduced the organicconsumption during denitrification. the developed novel functional septic tank achieved efficient of TN and TP removal from the low-C/N fecal sewage.