Nano-sized　C-S-H　crystal　seed　nucleating　agent　can　effectively　promote　the　hydration　process　of　cement　and　improve　the　early　strength　of　cementitious　composites　via　providing　some　nucleation　sites　for　cement　hydration　products.　The　calcium-silica　molar　ratio　can　affect　the　early　strength　effect　of　nano-sized　C-S-H　crystalline　seeds　on　cement,　but　the　specific　influence　law　is　still　controversial.　In　this　paper,　the　effect　of　calcium-silica　molar　ratio　on　the　size　and　morphology　of　nano-sized　C-S-H　crystalline　species　and　their　early　strength　effects　on　cement　was　investigated　by　X-ray　fluorescence　spectroscopy,　multiple　light　scattering　analysis,　dynamic　light　scattering　analysis,　X-ray　diffraction,　transmission　electron　microscopy,　cement　hydration　exotherm　and　strength　tests,　and　the　mechanism　of　calcium-silica　molar　ratio　affecting　the　early　strength　of　nano-sized　C-S-H　crystalline　species　on　cement　was　elucidated.　The　results　show　that　the　nucleation　efficiency　of　C-S-H　nano-crystals　can　be　improved　as　calcium　and　silicon　molarity　is　increased.　The　size　of　C-S-H　nano-crystals　gradually　becomes　smaller　and　the　dispersion　stability　of　suspension　improves　when　calcium-silica　molar　ratio　increases　from　1.0　to　1.7.　Also,　the　morphology　of　C-S-H　nano-crystalschanges　from　spherical　to　tin　foil,　and　the　stacking　between　the　crystals　decreases　and　the　layer　thickness　becomes　thinner　when　calcium-silica　molar　ratio　increases.　The　C-S-H　nano-crystals　can　promote　the　development　of　cement　hydration　exothermic　rate　and　early　strength,　especially　within　the　age　of　1　d.　The　higher　the　calcium-silica　molar　ratio　is,　the　greater　the　acceleration　of　cement　hydration　exothermic　rate　by　C-S-H　nano-crystals　and　the　higher　the　early　compressive　strength　enhancement　will　be.　©　2022,　Editorial　Department　of　Journal　of　the　Chinese　Ceramic　Society.　All　right　reserved.