Aiming　at　the　problem　of　the　cement　hydration　shrinkage　phenomenon,　which　occurs　when　cement　seals　downhole　casing　in　the　process　of　Carbon　Capture,　Utilization,　and　Storage　(CCUS)　technology,　this　paper　proposes　a　method　of　sealing　the　casing　by　combining　threaded　casing　with　bismuth-tin　alloy.　The　effect　of　different　types　of　grooves　(square-,　trapezoidal-,　and　screw-threaded　grooves)　set　on　the　inner　surface　of　the　casing　on　the　gas　sealing　performance　of　the　alloy　plug　was　analyzed.　And　the　effect　of　the　overlay　pressure　on　the　gas　sealing　performance　of　the　alloy　plug　during　the　molding　process　was　analyzed.　The　experimental　results　show　that　under　0.2　MPa　overlay　pressure,　the　gas　breakthrough　pressure　values　of　alloy　plugs　in　square-threaded,　screw-threaded,　trapezoidal-threaded,　and　smooth　hole　casings　are　5,　3.7,　2.9,　and　1　MPa,　respectively.　When　the　pitch　in　the　screw-threaded　casing　is　half　of　the　original,　the　gas　breakthrough　pressure　value　of　the　alloy　plugs　in　the　casing　is　4.7　MPa.　And　after　the　application　of　0.2　MPa　overlay　pressure,　the　gas　sealing　performance　of　the　alloy　plugs　in　the　screw-threaded,　trapezoidal-threaded,　and　light　hole　casings　was　improved　by　220%,　230%,　and　100%,　respectively.　The　experimental　results　show　that　when　the　grooves　are　set　on　the　inner　surface　of　the　casing,　the　gas　flow　path　per　unit　length　of　the　alloy　plug-casing　interface　is　prolonged,　and　the　grooves　increase　the　degree　of　zigzagging　on　the　inner　surface　of　the　casing.　The　gas　sealing　performance　of　the　alloy　plugs　is　greatly　enhanced.　This　research　can　provide　theoretical　support　for　the　application　of　downhole　Carbon　Storage　using　Sn58Bi　in　casing.