With　fluorescence　spectroscopy　and　Fourier　transform　ion　cyclotron　resonance　mass　spectrometry　(FT-ICR　MS),　this　study　evaluated　the　performance　of　zero-valent　iron　(ZVI)　enhanced　anammox　process　for　treating　fulvic　acids　(FA)-containing　wastewater　and　investigated　the　fate　of　dissolved　organic　nitrogen　(DON)　at　the　molecular　level.　The　results　showed　that　ZVI　increased　the　total　organic　carbon　(TOC)　removal　rate　of　the　anammox　system　by　approximately　10%　and　reduced　the　organic　matter　fluorescence　intensity　by　21%.　Specifically,　microbial　humic-like　C1　and　terrestrial　humic-like　C4　components　were　preferentially　degraded　by　ZVI　among　the　fluorescence　components　(C1-C4).　Moreover,　ZVI　significantly　altered　the　transformation　pathways　of　DON　molecules　in　anammox.　The　number　of　precursors　molecular　formulas　increased　from　1617　to　2002,　attributed　to　the　elimination　of　high　molecular　weight　(MW)　(＞500　Da)　molecules.　Specifically,　DON　molecules　with　high　O/C　were　degraded　under　the　effect　of　ZVI,　while　some　high　MW　were　resisted.　The　original　products　generated　from　anammox　consortia　metabolism　and　FA　degradation　underwent　secondary　reactions　with　ZVI,　thereby　decreased　the　O/C　of　products　molecular　formulas.　Furthermore,　anammox　process　was　subjected　to　the　most　carboxylic　acid　reaction,　including　decarboxylation　and　reduction　of　carboxylic　acids.　For　CHON　molecules,　a　significant　number　of　reactions　involving　the　reduction　of　nitro　groups　contributed　to　the　reduction　of　wastewater　toxicity,　which　improved　the　overall　performance.