Based　on　the　principle　of　thermosyphon　and　combined　with　filling　subgrade　in　Tanggula　permafrost　regions　range,　the　cooling　effect　of　thermosyphon　on　filling　subgrade　was　analyzed　with　FEM　considering　thermal　conductivity　of　thermosyphon,　southern　and　northern　slopes　and　phase　change.　The　results　show　that　after　one　year　a　low　temperature　region　below　-0.5°C　with　about　8.6　m　diameter　will　form　at　the　bottom　of　southern　slope,　and　near　the　slope　toe　of　northern　slope　a　bar-like　low　temperature　region　below　-3°C　with　about　9.6　m　diameter　will　form.　In　the　third　year,　a　low　temperature　region　below　0.8°C　at　the　bottom　of　northern　slope　will　form.　Thermosyphon　has　good　cooling　effect,　which　can　prevent　the　permafrost　below　subgrade　from　thawing,　thus　ensuring　the　stability　of　subgrade.