This　paper　presents　a　cross-scale　prediction　of　the　dielectric　properties　of　long-term-cured　tricalcium　silicate　(C3S)　paste　specimens　and　investigated　the　effect　of　different　phase　geometry　models　on　the　prediction　results.　Firstly,　the　dielectric　properties　of　C3S　paste　specimens　cured　for　180　days　were　tested.　Based　on　tests　such　as　X-ray　diffraction　(XRD)　and　mercury　intrusion　porosity　(MIP),　the　types　of　phases　and　the　volume　fractions　of　individual　phases　in　the　C3S　paste　specimens　were　determined.　Subsequently,　the　dielectric　performance　of　the　phases　was　measured.　The　dielectric　performance　linkage　between　each　phase　and　the　C3S　paste　specimen　was　established　based　on　the　effective　medium　theory.　The　effects　of　three　morphological　models　of　the　phase　on　the　predicted　results　were　dissected.　The　results　showed　that　the　volume　fraction　and　dielectric　constant　of　calcium　silicate　hydrates　(C-S-H)　gel　were　significantly　higher　than　those　of　other　phases　in　the　C3S　paste　specimens.　Among　the　three　computational　models　of　phase　geometry,　the　standard　spherical　phase　model　produced　the　best　prediction.　The　prediction　results　of　the　standard　spherical　model　improved　the　accuracy　by　more　than　45.8%　compared　with　that　of　the　oblate　phase　model　and　the　prolate　phase　model.　Among　the　phases,　the　trend　of　the　dielectric　constant　of　C-S-H　gels　with　frequency　was　the　most　similar　to　the　results　obtained　by　the　three　prediction　models.　©　2023　American　Society　of　Civil　Engineers.