By　combining　first-principles　calculations　and　experiments,　the　effects　of　Hf　doping　on　the　stability　and　magnetic　properties　of　the　metastable　SmCo7　alloy　were　studied.　It　is　found　that　the　single　TbCu7-type　phase　can　be　stabilized　well　by　Hf　doping　when　the　Co-2e　sites　are　occupied　in　the　lattice　structure.　However,　if　Hf　occupies　the　Co-3g　sites,　destabilization　of　the　SmCo7　phase　may　occur.　Moreover,　Hf　doping　changes　the　partial　density　of　states　of　Sm　atoms　in　the　vicinity　of　Co-2e　sites,　which　causes　a　decrease　in　the　net　magnetic　moments　and　hence　a　decrease　in　the　saturation　magnetization.　The　experimental　results　confirmed　the　calculation　results　of　the　phase　stability　and　magnetic　performance　of　the　Hf-doped　SmCo7　alloys.