Feammox, one of the potential pathways for nitrogen loss in the environment, plays an essential role in nitrogen cycling and provides new ideas for the biological denitrification of wastewater. However, the Feammox reaction has low nitrogen removal efficiency and stagnates due to insufficient Fe(III) sources. It strongly depends on an Fe(III) source supply, significantly limiting its development. In this study, a synergistic nitrogen removal system using Feammox and Nitrate-Dependent Fe(II) Oxidation (NDFO) driven by NO₃⁻-N was constructed within an organic carbon environment. It uses the synergy between Feammox and NDFO to improve nitrogen removal. The removal efficiency of NH₄⁺-N reaches over 70% in stages III-V, with a maximum removal efficiency of 89.4%. NH₄⁺-N oxidation and Fe(III) reduction are positively coupled in the Feammox reaction. The Fe(II)/Fe(III) cycle process driven by Feammox and NDFO improves the utilization of the iron source, thus guaranteeing the sustainability of the NH₄⁺-N oxidation reaction. In addition, the organic carbon environment also enriched NDFO bacteria (Thermomonas and Acinetobacter) and increased the reaction rate of NDFO, which enhanced the transformation of Fe(II). We improved the nitrogen removal efficiency of Feammox and provided a new approach for nitrogen removal in wastewater treatment.