The　protein　corona　has　gained　much　attention　in　the　field　of　nano-biomedicine　and　has　expanded　from　applications　in　the　biological　field　to　the　ecosphere.　However,　the　bio-corona　(extracellular　protein　corona)　composed　of　nano-quantum　dots　(CdSe@ZnS)　and　extracellular　proteins　in　an　activated　sludge　system　was　limited　by　the　inability　to　identify　the　composition　and　molecular　structure　of　extracellular　proteins.　Herein,　extracellular　proteins　(EP)　were　extracted　from　the　active　sludge　(AS)　system　and　purified　by　using　a　novel　method　(modified-ammonium　sulfate　precipitate)　and　then　identified　by　proteomic　technology.　The　interaction　between　nano-quantum　dots　and　extracellular　protein　was　investigated　with　multi-spectroscopic　technology　and　microscopic　analysis.　The　results　revealed　that　97　protein　groups　were　detected　and　most　of　their　molecular　functions　were　related　to　the　cation　binding　activity.　The　self-aggregation　effect　of　protein　particles　and　the　formation　of　the　bio-corona　were　observed.　Meanwhile,　alpha-helical　structures　of　EPs　in　active　sludge　were　converted　into　beta-sheets　conformationviaelectrostatic　and　hydrogen　bonding　processes,　with　the　addition　of　nano-quantum　dots,　resulting　in　decreased　fluorescence　intensities　for　proteins.　This　finding　not　only　provided　a　novel　method　for　the　purification　of　EP　from　extracellular　polymeric　substances,　but　also　provided　an　insight　into　the　interaction　between　NPs　and　actual　EP　in　the　AS　system.