The　combined　utilization　of　mineral　accelerators　and　nano-seeding　materials　is　a　novel　method　to　promote　the　early　strength　of　cement-based　materials.　In　this　paper,　the　effects　of　nano-C-S-H　seed　(NCS)　on　the　early　compressive　strength　of　the　Portland　cement　(PC)-　calcium　sulfoaluminate　cement　(CSA)　binder　were　investigated.　The　results　showed　that　NCS　and　CSA　synergistically　contributed　to　the　early　strength　of　PC.　In　detail,　a　326.3%　increase　in　the　10　h　compressive　strength　of　PC　paste　was　obtained　through　the　addition　of　NCS　(2　wt%)　and　CSA　(5%)　in　common.　This　was　higher　than　the　sum　of　the　increases　observed　with　the　single　additions　of　CSA　(157.9%)　or　NCS　(87.6%),　with　the　same　above　dosage,　in　PC.　Meanwhile,　the　early　strength　enhancement　effects　of　NCS　and　CSA,　when　used　together　in　PC,　lasted　longer　than　the　effects　of　either　used　alone.　Moreover,　the　synergetic　effect　mechanism　was　analyzed　by　isothermal　calorimeter,　QXRD,　TGA,　MIP,　and　SEM　techniques.　The　calorimetry,　XRD,　and　TGA　results　demonstrated　that　the　synergistic　mechanism　was　associated　with　the　synergistic　promotion　effects　of　CSA　and　NCS　on　the　hydrates.　The　fast　hydration　of　CSA　produced　large　amounts　of　ettringite　and　also　consumed　partial　free　water　to　promote　the　performance　of　the　seeding　effect　of　NCS　which,　simultaneously,　further　accelerated　the　precipitation　of　C-S-H　gel　and　CH.　The　high　alkie　environment　was　also　beneficial　for　the　continuous　generation　of　ettringite.　In　addition,　the　results　of　MIP　and　SEM　measurements　showed　that　the　micro-filling　effect　of　NCS　significantly　optimized　the　pore　structure　of　a　PC-CSA　blend-hardened　paste.　Thus,　the　synergistic　strength　enhancement　effects　of　CSA　and　NCS　on　PC　were　attributed　to　the　matching　of　the　promotion　of　hydration　generation　and　the　optimization　of　pore　structures　in　hardening　cement　paste.　The　results　of　this　article　provide　a　new　approach　to　achieving　the　rapid　development　of　the　early　strength　of　cementitious　materials,　with　potential　applications　in　precast　concrete　and　low-temperature　construction.