The　environmental　risk　of　microplastics　(MPs)　in　aerobic　granular　sludge　(AGS)　system　is　unclear.　This　study　evaluates　the　effects　of　non-biodegradable　polyvinyl　chloride　microplastics　(PVC-MPs)　and　biodegradable　polylactic　acid　microplastics　(PLA-MPs)　on　AGS　systems.　The　results　showed　that　both　destroyed　the　performance　of　AGS　systems,　with　PVC-MPs　achieving　this　by　disrupting　the　AGS　structure,　while　PLA-MPs　mainly　by　causing　the　expansion　of　filamentous　bacteria　induced　through　the　stimulation　by　lactic　acid　metabolite　(R0:　5.52　+/-　0.49　mu　g/L;　RPLA5:　11.67　+/-　0.56　mu　g/L).　Moreover,　both　MPs　inhibited　nitrogen　removal　by　disrupting　partial　nitrification　and　endogenous　denitrification　and　suppressed　key　microbes　such　as　Candidatus　Competibacter　and　Nitrosomonas.　Metabolic　pathway　analysis　and　molecular　docking　have　further　confirmed　the　mechanisms　by　which　MPs　affect　critical　metabolic　pathways　and　key　enzymes.　Consequently,　the　hazards　of　biodegradable　MPs　to　the　stable　operation　of　sewage　treatment　plants　should　also　be　of　concern.