Nd-Fe-B　sintered　magnets　with　ultrahigh　coericivity　of　47.1　kOe　and　maximum　energy　product　of　38.5　MGOehave　been　successfully　prepared　by　TbH3　nanoparticles　grain　boundary　diffusion　(GBD)　process.　Microstructural　observations　show　that　Tb　enriches　in　the　outer　regions　of　2:　14:　1　matrix　phase　grains,　forming　a　core-shell　structure.　High　temperature　magnetic　domain　evolution　observations　indicate　that　reversed　domains　tend　to　nucleate　at　the　outer　regions　of　2:　14:　1　matrix　phase　grains　at　200　degrees　C,　while　the　Tb-rich　shells　show　high　magnetocrystalline　anisotropy　improving　the　nucleation　field　at　outer　regions,　leading　to　enhancement　of　high　temperature　magnetic　performance.