The　correlation　of　the　lack　in　multivalent　cations　with　hydrolase　activity　and　microbial　community　in　anaerobic　fermentation　of　waste　activated　sludge　was　investigated　in　this　study.　It　was　demonstrated　that　considerable　solid　phase　reduction　of　41　%　(7.87　g/L)　was　achievable　through　a　cation　exchange　resin-enhanced　anaerobic　fermentation　of　4　days.　The　protease　and　α-glucosidase,　especially　α-glucosidase,　were　easily　influenced　by　a　lack　in　multivalent　cations.　Furthermore,　species　abundance　and　diversity　of　microbial　community　gradually　decreased.　Meanwhile,　the　bacteria　community　structure　presented　obvious　dynamic　shifts.　Ruminococcaceae_UCG_009,　Bacteroides　and　Macellibacteroides　responsible　for　organic　matter　biodegradation　and　SCFAs　production　became　dominant　bacteria　in　cation　exchange　resin-enhanced　anaerobic　fermentation,　which　was　less　influenced　by　the　lack　in　multivalent　cations,　while　the　SCFA　consumers　(e.g.　methanogens)　were　inhibited　with　reduced　abundances　due　to　their　susceptibility　to　the　lack　in　multivalent　cations.　Redundancy　analysis　revealed　that　the　lack　in　multivalent　cations　were　responsible　for　the　microbial　community　evolution,　which　was　proved　by　the　high　Grey　relational　coefficients　(0.747−0.820)　and　significant　negative　Spearman　coefficients　(−0.5798　to　−0.9429)　between　multivalent　cation　and　microbial　community.　Obviously,　the　cation　exchange　resin-induced　removal　of　multivalent　cations　reduced　enzyme　activity　and　modified　microbial　community　structure,　which　created　a　beneficial　environment　for　enhancing　anaerobic　fermentation.　©　2020　Elsevier　B.V.