While　numerous　studies　on　catalysts　with　varying　metal　site　sizes　in　Fenton-like　systems　have　explored　synergistic　mechanisms　between　single　atoms　(SAs)　and　nanoparticles　(NPs),　the　axial　enhancement　mechanism　of　NPs　toward　SAs　remains　underexplored.　Here,　we　revealed　the　mechanism　by　which　nitrogen-doped　graphitic　carbon　encapsulated　NPs　axially　enhance　the　activation　of　surface　SAs　over　peroxymonosulfate　(PMS).　A　novel　CoNPs-SAs@N-C　catalyst　coexisting　with　Co　SAs　and　encapsulated　Co　NPs　was　synthesized,　in　which　the　internalization　of　Co　NPs　accelerated　the　interfacial　mass　transfer　rate　resulting　in　4.8-fold　increase　in　the　degradation　efficiency　of　the　composite　catalytic　system　relative　to　the　single-atom　system.　Density　functional　theory　(DFT)　calculations　showed　that　Co　NPs　can　enhance　the　interfacial　electron　transfer　rate　of　surface　Co　SAs　and　strengthen　the　interaction　of　Co　SAs　with　PMS　to　produce　more　1O2,　besides　fundamentally　altering　the　coordination　environments　and　electronic　structures　of　Co　SAs.　Additionally,　the　composite　system　showed　exceptional　prospects　for　practical　applications,　with　long　term　stability　for　the　treatment　of　real　wastewater.　Our　findings　deepen　the　understanding　of　nano-single-atom　composite　catalysis　and　may　inspire　innovations　in　emerging　water　purification　technologies　and　other　multiphase　catalytic　applications.　©　2025　Elsevier　B.V.