Starting　with　the　ingot　with　a　nominal　stoichiometric　composition　of　SmCo9.8,　the　nanocrystalline　bulk　with　ultrafine　nanograin　structure　was　prepared　by　a　route　combing　ball　milling　and　spark　plasma　sintering.　The　phase　formation,　microstructure,　crystal　lattice　characteristics,　and　magnetic　performance　of　the　nanocrystalline　SmCo9.8　alloy　were　investigated.　The　TbCu7-type　solid　solution　of　the　SmCo9.8　composition　was　obtained,　and　the　crystal　structure　of　the　nanocrystalline　1:9.8　H　was　constructed.　The　magnetic　features　were　disclosed　through　nanostructuring　to　obtain　the　single　metastable　1:　9.8　H.　It　was　found　that　the　nanocrystalline　SmCo9.8　alloy　has　high　saturation　magnetization　and　Curie　temperature.　The　study　presents　a　new　understanding　of　the　nanoscale-stabilized　TbCu7-type　solid　solution　of　the　SmCo9.8　composition　and　may　promote　the　development　of　SmCo9.8-type　alloys　as　candidates　for　the　high-temperature　permanent　magnets,　based　on　the　coercivity　improvement.　(C)　2011　American　Institute　of　Physics.　[doi:10.1063/1.3671612]