C-S-H-PCE　nanocomposites　(CPNs)　serving　as　nucleation　sites　are　a　promising　material　to　accelerate　the　cement　hydration　and　gain　high　early　strength　for　cementitious　materials.　This　study　aimed　to　investigate　the　effects　of　CPNs　on　the　properties　and　hydration　of　cement　mortar　under　different　water-to-cement　(w/c)　ratios.　CPNs　were　prepared　via　the　co-precipitation　method　in　MAPEG-PCE　solution　and　characterized　by　means　of　XRD,　FT-IR,　DLS,　TEM,　TGA,　and　TOC.　The　mechanism　and　effect　of　CPNs　on　the　early　hydration　of　cement　mortar　with　w/c　ratios　of　0.50,　0.40,　and　0.35　were　assessed　in　terms　of　mechanical　properties,　isothermal　calorimetry,　setting　time　XRD,　TGA,　SEM,　and　MIP.　The　results　showed　that　CPNs　significantly　promoted　the　early　strength　development　of　mortar　and　a　higher　enhancement　ratio　was　brought　at　a　lower　w/c　ratio.　Calorimetry　and　setting　results　also　showed　a　greater　hydration　acceleration　of　samples　dosed　CPNs　with　lower　w/c　ratio.　From　the　analysis　of　XRD　and　TGA,　the　content　of　CH　and　C-S-H　in　the　samples　dosed　CPNs　increased　with　the　decrease　of　w/c　ratio　in　6　h,　while　exhibited　an　opposite　trend　in　12　h　and　3　d.　MIP　and　SEM　results　showed　that　CPNs　led　to　a　refinement　of　pore　structure　and　dense　morphology,　especially　at　a　low　w/c　ratio.　Moreover,　the　underlying　acceleration　mechanism　of　cement　hydration　versus　w/c　ratio　was　that　the　seeding　ability　was　enhanced　for　the　low　distance　between　cement　and　CPNs　at　a　low　w/c　ratio.　According　to　this　research,　the　use　of　CPNs　may　be　more　practical　in　high-strength　concrete.