This　study　proposed　a　cation-regulation　strategy　based　on　metal　ion　removal　coupled　Na+-regulation　for　enhancing　anaerobic　fermentation　of　waste　activated　sludge.　The　optimal　treatment　condition　was:　cation-exchange　resin　dosage　of　1.75　g/g　SS　for　1-day　treatment,　followed　by　Na+-enhanced　anaerobic　fermentation　at　NaCl　concentration　of　20　g/L.　The　CER　induced　sludge　solubilization　and　the　Na+-regulation　treatment　triggered　secondary　hydrolysis　of　CER-solubilized　sludge,　causing　remarkable　sludge　disintegration　and　extracellular　polymeric　substance　(EPS)　disruption.　Numerous　SCOD　of　6588　mg/L　(SCOD/TCOD　=　40.6%)　was　released　within　2　days,　and　the　short-chain　fatty　acids　(SCFAs)　of　439.9　mg　COD/g　VSS　was　produced　through　4-day　anaerobic　fermentation.　More　than　59%　of　the　SCFAs　was　composed　of　acetate　and　propionate.　Nitrogen-free　organic　matters　(i.e.　SCFAs　and　carbohydrates)　accounted　for　77.9%　of　SCOD,　while　considerable　sludge　solid　reduction　(51.6%　of　total　VSS)　was　achievable,　which　was　beneficial　for　fermentative　liquid　utilization　and　sludge　disposal.　©　2021　Elsevier　Ltd