The　mechanism　of　the　effect　of　a　Ca-rich　environment　on　the　reaction　process　and　the　molecular　structure　of　the　magnesium　oxide　(MgO)-activated　SiO2　reaction　product　are　described　in　this　research.　In　the　experimental　study,　MgO,　silica　fume,　and　calcium　oxide　(CaO)　were　used　as　raw　materials　to　prepare　a　calcium-magnesium　coupling　excited　SiO2　system　with　different　Ca:Mg　molar　ratios.　The　samples　were　characterized　by　X-ray　diffraction,　thermogravimetry/derivative　thermogravimetry,　inductively　coupled　plasma　mass　spectroscopy,　transmission　electron　microscopy,　and　29Si　nuclear　magnetic　resonance.　A　higher　Ca:Mg　molar　ratio　(above　0.179:1)　inhibited　magnesium　silicate　hydrate　gel　formation,　while　a　lower　ratio　(less　than　0.09:1)　promoted　magnesium　silicate　hydrate　gel　formation.　The　amount　of　Ca2+　and　Mg2+　presented　in　the　pore　solution　in　the　Ca-rich　environment　was　not　sufficient　to　react　with　silicate　ions　(H2SiO2-4　and　H3SiO-4)　to　form　gel,　leading　to　surplus　SiO2.　Changes　in　the　Ca2+　concentration　in　the　pore　solution　affected　Mg2+　and　silicate　ions　behavior.　The　hydration　of　low　amounts　of　CaO　provided　ionization　products　of　Ca2+　and　OH-　ions,　MgO　and　CaO　were　hydrolyzed,　and　less　ionized　OH-　was　consumed　by　silicate　ions.　The　hydration　and　ionization　of　MgO　increased　the　Mg2+　concentration,　while　the　silicate　ions　concentration　decreased.　However,　excess　OH-　ions　produced　by　hydration　and　ionization　with　high　amounts　of　CaO　exhibited　opposite　effects,　subsequently　impacting　the　calcium-magnesium　coupling　excited　SiO2　system.　Thermodynamic　calculations　revealed　that　the　magnesium　silicate　hydrate　gel　was　more　stable　than　the　calcium　silicate　hydrate　gel,　and　the　influence　of　various　Ca-rich　environments　on　the　MgO-activated　SiO2　reaction　process　was　further　studied.