Daytime　radiative　cooling　technology　offers　a　low-carbon,　environmentally　friendly,　and　nonpower-consuming　approach　to　realize　building　energy　conservation.　It　is　important　to　design　materials　with　high　solar　reflectivity　and　high　infrared　emissivity　in　atmospheric　windows.　Herein,　a　porous　calcium　silicate　composite　SiO2　aerogel　water-borne　coating　with　strong　passive　radiative　cooling　and　high　thermal　insulation　properties　is　proposed,　which　shows　an　exceptional　solar　reflectance　of　94%,　high　sky　window　emissivity　of　96%,　and　0.0854　W/m·K　thermal　conductivity.　On　the　SiO2/CaSiO3　radiative　cooling　coating　(SiO2−CS-coating),　a　strategy　is　proposed　to　enhance　the　atmospheric　window　emissivity　by　lattice　resonance,　which　is　attributed　to　the　eight-membered　ring　structure　of　porous　calcium　silicate,　thereby　increasing　the　atmospheric　window　emissivity.　In　the　daytime　test　(solar　irradiance　900W/m2,　ambient　temperature　43　°C,　wind　speed　0.53　m/s,　humidity　25%),　the　temperature　inside　the　box　can　achieve　a　cooling　temperature　of　13　°C　lower　than　that　of　the　environment,　which　is　30　°C,　and　the　theoretical　cooling　power　is　96　W/m2.　Compared　with　the　commercial　white　coating,　SiO2−CS-coating　can　save　70　kW·h　of　electric　energy　in　1　month,　and　the　energy　consumption　is　reduced　by　36%.　The　work　provides　a　scalable,　widely　applicable　radiative-cooling　coating　for　building　comfort,　which　can　greatly　reduce　indoor　temperatures　and　is　suitable　for　building　surfaces.　©　2024　American　Chemical　Society.