Aimed　at　the　problem　of　gas　flurries　in　carbon　dioxide　(CO2)　geologic　sequestration　in　the　wellbore,　this　paper　proposes　a　sealing　method　in　which　the　downhole　casing　is　processed　with　threaded　grooves　and　then　plugged　with　a　low-melting-point　alloy　plug.　Based　on　this　method,　a　small-scale　experimental　setup　was　developed　for　alloy　plug　molding　and　gas　sealing　in　this　study.　Molding　and　gas　sealing　experiments　with　Sn58Bi　alloy　plugs　inside　casings　with　different　surface　morphologies　were　carried　out.　The　gas　leakage　pathway　was　determined.　The　microstructure　of　the　interface　between　the　alloy　plug　and　casing　was　analyzed　using　an　optical　microscope.　The　influence　of　the　inner　surface　roughness,　threaded　groove,　length-to-diameter　ratio,　and　ambient　temperature　on　the　gas　sealing　performance　of　the　alloy　plugs　was　analyzed.　The　experimental　results　show　that,　with　an　increase　in　ambient　temperature,　the　gas　sealing　performance　of　the　casing　increases　significantly;　when　the　inner　surface　of　the　casing　is　processed　through　threaded　grooves,　the　gas　sealing　performance　is　better　than　with　smooth　hole　casing;　the　gas　sealing　performance　of　the　alloy　plug　presents　an　obvious　linear　positive　correlation　with　their　length-to-diameter　ratio.　This　research　provides　theoretical　support　for　downhole　CO2　plugging　using　Sn58Bi　in　the　casing.