The　grain　boundary　diffusion　(GBD)　technology　effectively　utilizes　heavy　rare　earth　(HRE)　elements　to　improve　the　coercivity　of　sintered　Nd-Fe-B　magnet.　Significantly,　clarifying　its　coercivity　improvement　mechanism　is　essential　for　further　optimizing　the　process　and　performance.　Through　comparative　analysis　with　commercial　conventional　magnets　(CSH)　processing　equivalent　coercivity,　this　study　investigated　the　specific　mechanism　by　which　the　GBD　method　enhances　the　coercivity　of　HRE　elements　in　an　efficient　manner.　To　achieve　the　same　coercivity　(∼21.4　kOe),　GBD　magnets　contained　only　0.25　wt%　Tb,　whereas　CSH　magnets　had　1.17　wt%　Dy　and　1.18　wt%　Tb.　The　microstructure　analysis　revealed　that　the　Tb　element　in　the　GBD　magnet　was　concentrated　in　the　outer　layer　of　the　grain,　constituting　17.37　wt%　of　the　total　rare　earth　content.　While,　in　CSH　magnets,　the　HRE　element　in　the　main　phase　grains　accounted　for　only　9.58　wt%　of　the　total　rare　earth　elements,　including　Dy　(3.83　wt%)　and　Tb　(5.75　wt%).　The　characteristic　core-shell　structural　grains　in　GBD　magnet　also　endowed　it　with　an　uneven　magnetic　domain　structure　and　a　more　concentrated　“abrupt”　magnetization　reversal.　Based　on　the　characterization　results　the　nucleation　positions　of　the　two　types　of　magnets　were　analyzed　by　fitting　Hci/Ms　and　Ha/Ms.　The　results　can　serve　as　a　guide　for　enhancing　coercivity　in　grain　boundary　diffusion　sintered　Nd-Fe-B　magnets,　aiding　in　process　and　property　optimization,　and　advancing　the　understanding　of　nucleation　type　mechanisms.　©　2024　Elsevier　Inc.