Improving　the　coercivity　of　high　La/Ce　content　multi-main-phase　(MMP)　sintered　magnets　is　crucial　for　promoting　the　use　of　La/Ce　elements　in　permanent　magnets.　In　this　work,　we　used　a　novel　strategy　to　accurately　manipulate　the　chemical　heterogeneity　and　grain　boundary　(GB)　structures　of　MMP　Nd-La-Ce-Fe-B　sintered　magnets,　namely,　by　adjusting　the　composition　of　the　LaCe-free　alloys.　We　obtained　an　ultrahigh　coercivity　value　of　13.75　kOe　for　the　MMP-LaCe35　(LaCe　accounted　for　35　wt.%　of　total　rare　earth)　magnet.　This　was　attributed　to　the　effect　of　Al-Cu-Ga　element　addition　in　LaCe-free　alloys　toward　enhancing　chemical　heterogeneity　(thicker　Nd-rich　shells)　and　optimizing　the　GB　structures　(continuous　lamellar　GBs).　The　former　had　a　higher　anisotropy　field　(HA)　value,　which　enhanced　the　nucleation　field,　while　the　latter　had　a　lower　Fe　concentration,　which　improved　the　magnetic　isolation　effect.　Based　on　the　above　mechanisms,　a　coercivity　of　12.09　kOe　was　attained　for　the　MMP-LaCe40　magnet　produced　utilizing　an　alloy　with　the　same　composition.　In　addition,　reducing　the　Nd　content　while　maintaining　the　addition　of　Al-Cu-Ga　elements　in　the　LaCe-free　alloy　proved　that　adding　Al-Cu-Ga　elements　improved　the　GB　phase　wettability　of　the　MMP　magnets,　thereby　forming　continuous　lamellar　GBs　to　enhance　coercivity.　Our　findings　revealed　that　the　enhanced　chemical　heterogeneity　also　effectively　improved　the　coercivity　temperature　stability　of　the　MMP　magnets.　This　study　provided　an　effective　and　feasible　strategy　for　microstructure　manipulation　to　prepare　ultrahigh　coercivity　MMP-sintered　magnets　with　higher　LaCe　content,　which　is　crucial　for　promoting　the　comprehensive　utilization　of　rare　earth　resources.