The　sintering　of　osmium　is　critical　for　the　preparation　of　raw　material　targets　for　film　coating,　which　is　the　main　application　area　of　osmium.　In　order　to　get　a　better　understanding　of　the　intrinsic　mechanism　of　densification　of　osmium,　a　serial　study　on　the　sintering　behavior　of　osmium　has　been　made　in　this　study.　By　the　master　sintering　curve　(MSC)　and　constant　heating　rate　(CHR)　method,　the　sintering　activation　energy　of　nanosized　osmium　is　evaluated　to　be　about　340　kJ/mol,　which　is　higher　than　most　other　metals.　The　density-functional　theory　calculation　indicates　the　higher　energy　barrier　of　the　surface　atom　and　vacancy　migration　and　lacking　migration　tunnel　of　inner　point　vacancies.　For　example,　the　diffusion　of　osmium　atoms　on　the　surface　of　particles　is　mainly　limited　by　Os　(1010),　which　has　an　energy　barrier　as　high　as　1.14　eV,　that　is　higher　than　the　W　atom　on　W　(110)　of　0.99　eV.　The　vacancy　migration　energy　barrier　inside　osmium＇s　grains　is　higher　than　3.0　eV,　while　that　of　W　is　only　1.7　eV.　This　means　that　it　is　more　difficult　for　osmium　to　achieve　a　high　density　compared　with　W,　which　is　consistent　with　the　experimental　results.　Accordingly,　the　proposed　strategy　provides　a　new　opportunity　to　design　a　sintering　process　for　target　fabrication　with　excellent　properties　for　various　applications.