This　study　successfully　established　Iron　Sulfide-Mediated　mixotrophic　Partial　Denitrification/Anammox　system,　achieving　nitrogen　and　phosphorus　removal　efficiency　of　97.26%　and　78.12%,　respectively,　with　COD/NO3--N　of　1.00.　Isotopic　experiments　and　X-ray　Photoelectron　Spectroscopy　analysis　confirmed　that　iron　sulfide　enhanced　autotrophic　Partial　Denitrification　performance.　Meanwhile,　various　sulfur　valence　states　functioned　as　electron　buffers,　reinforcing　nitrogen　and　sulfur　cycles.　Microbial　community　analysis　indicated　reduced　heterotrophic　denitrifiers　(OLB8,　OLB13)　under　lower　COD/NO3--N,　creating　more　niche　space　for　autotrophic　bacteria　and　other　heterotrophic　denitrifiers.　The　prediction　of　functional　genes　illustrated　that　iron　Sulfide　upregulated　genes　related　to　carbon　metabolism,　denitrification,　anammox　and　sulfur　oxidation-reduction,　facilitating　the　establishment　of　carbon-nitrogen-sulfur　cycle.　Furthermore,　this　cycle　primarily　produced　electrons　via　nicotinamide　adenine　dinucleotide　and　sulfur　oxidation-reduction　processes,　subsequently　utilized　within　the　electron　transfer　chain.　In　summary,　the　Partial　Denitrification/Anammox　system　under　the　influence　of　iron　sulfide　achieved　effient　nitrogen　removal　by　expediting　electron　transfer　through　the　carbon-nitrogen-sulfur　cycle.