The　beneficial　effects　of　biopolymers　have　recently　been　paid　much　attention,　including　improved　coagulation　performance,　adsorb　metal　cations.　Ultrafiltration,　an　important　advanced　treatment　process　for　drinking　water,　often　faces　serious　membrane　fouling　caused　by　biopolymers.　Whether　biopolymers　on　ultrafiltration　membranes　surface　can　be　collected　for　use　in　coagulation　units　is　little　known,　and　the　interaction　mechanism　between　water　quality,　biopolymer　components　and　microorganisms　has　not　been　investigated.　In　this　study,　we　ran　three　groups　of　reactors　with　different　water　quality　of　influent　in　parallel,　and　compared　the　difference　in　coagulation　aiding　behavior　and　characteristics　of　biopolymers　collected　from　different　membrane　units.　The　results　showed　that　the　molecular　weight　distribution　and　functional　groups　of　biopolymers　collected　by　different　membrane　units　were　similar,　but　their　component　concentrations　were　different,　among　which　polysaccharide　was　the　key　component　determining　the　coagulation-promoting　performance　of　biopolymers.　The　water　quality　of　influent　affected　microbial　community　composition　(e.g.,　keystone　taxa)　and　microbial　network　characteristics　(connectivity　and　complexity)　in　the　cake　layer　of　membrane.　The　low-nutrient　environment　of　drinking　water　was　more　conducive　to　the　complexity　and　stability　of　the　microbial　network　in　the　cake　layer　of　the　membrane,　and　promoted　the　secretion　of　more　polysaccharides　by　bacteria　(e.g.,　Reyranella　and　Sphingopyxis).　Our　findings　provide　important　implications　for　in　situ　enrichment,　extraction　and　reuse　of　natural　biopolymers　in　drinking　water　treatment　plants.