The　cytochrome　C　(Cyt　c)　mediated　electron　transport　system　is　crucial　in　anaerobic　ammonia-oxidizing　granular　sludge　(AnGS).　Micro(nano)plastics　(MNPs)　have　received　much　attention　due　to　their　strong　biotoxicity,　but　the　mechanism　of　MNPs　effect　on　electron　transport　in　the　AnGS　system　is　not　clear.　This　study　investigated　the　response　mechanism　of　the　electron　transport　system　of　AnGS　when　exposed　to　poly　ethylene　terephthalate　micro(nano)plastics　(PET-MNPs)　at　different　concentrations　(0　mg/L,　1　mg/L,　100　mg/L,　500　mg/L)　and　particle　sizes　(80　mu　m,　300　nm).　The　results　showed　that　PET-MNPs　significantly　inhibited　the　nitrogen　removal　efficiency.　Similarly,　the　electron　transfer　activity　of　AnGS　exposed　to　high　concentrations　of　PET-MNPs　decreased　by　72.7　%　and　34.3　%,　respectively,　compared　to　control　group　(0　mg/L).　The　high-throughput　and　metagenomic　results　showed　that　PET-MNPs　suppressed　the　abundance　of　anaerobic　ammonium　oxidizing　bacteria　(Candidatus　Kuenenia　and　Candidatus　Brocadia),　energy　pathway,　electron　transport　pathway　and　the　Cyt　c-generating　genes.　Furthermore,　the　molecular　docking　results　showed　that　PET-MNPs　were　easily　and　stably　bound　to　key　proteins　in　both　the　extracellular　and　intracellular　electron　transport　pathways.　Among　them,　Cyt　c　was　the　most　easily　bound　protein　to　PET-MNPs　in　the　electron　transport　system　(binding　energy　of　-8.8　kcal/mol)　and　molecular　dynamics　simulations　also　verified　this　result.　In　addition,　the　Cyt　c　content　of　AnGS　exposed　to　the　high　concentration　group　decreased　by　78.49　%　(NPs　group)　and　73.40　%　(MPs　group),　respectively.　In　conclusion,　PETMNPs　can　cause　disruption　of　the　electron　transport　system　of　AnGS　by　inactivating　the　protein　by　changing　its　conformation　and　inhibiting　the　expression　of　related　functional　genes.