The　combination　of　dual-main-phase　(DMP)　(Nd,　Ce)-Fe-B　magnets　and　grain　boundary　diffusion　process　(GBDP)　is　currently　a　research　topic　for　obtaining　high-cost　performance　materials　in　rare　earth　permanent　magnet　fields.　The　novel　structural　features　of　GBDP　(Nd,　Ce)-Fe-B　magnets　give　a　version　of　different　domain　reversal　processes　from　those　of　non-diffused　magnets.　In　this　work,　the　in-situ　magnetic　domain　evolution　of　the　DMP　magnets　was　observed　at　elevated　temperatures,　and　the　temperature　demagnetization　and　coercivity　mechanism　of　the　GBDP　dual-main-phase　(Nd,　Ce)-Fe-B　magnets　are　discussed.　The　results　show　that　the　shell　composition　of　different　types　of　grains　in　DMP　magnets　is　similar,　while　the　magnetic　microstructure　results　indicate　the　Ce-rich　grains　tend　to　demagnetize　first.　Dy-rich　shell　with　a　high　anisotropic　field　caused　by　GBDP　leads　to　an　increase　in　the　nucleation　field,　which　enhances　the　coercivity.　It　is　found　that　much　more　grains　exhibit　single　domain　characteristics　in　the　remanent　state　for　GBDP　dual-main-phase　(Nd,　Ce)-Fe-B　magnets.　In　addition,　the　grains　that　undergo　demagnetization　first　are　Ce-rich　or　Nd-rich　grains,　which　is　different　from　that　of　non-diffused　magnets.　These　results　were　not　found　in　previous　studies　but　can　be　intuitively　characterized　from　the　perspective　of　magnetic　domains　in　this　work,　providing　a　new　perspective　and　understanding　of　the　performance　improvement　of　magnetic　materials.　©　2024