In　nuclear　reactors,　Silicon　carbide　fiber　reinforced　silicon　carbide　matrix　(SiCf/SiC　CMC)　cladding　tubes　are　susceptible　to　circumferential　damage　due　to　internal　gas　pressure　expansion.　However,　due　to　its　complex　spatial　fiber　winding　structure,　investigating　circumferential　tensile　failure　under　extreme　temperatures　is　challenging.　Therefore,　using　cross-scale　methods　and　experiments　from　20　°C　to　1100　°C,　this　study　examined　circumferential　damage　at　macro,　micro,　and　nanoscale　levels.　Specifically,　as　the　temperature　increases,　the　material　still　maintains　excellent　structural　stability;　at　1100　°C,　the　critical　damage　load　decreases　by　72.5　%　and　the　critical　displacement　increases　by　197.1　%.The　＇　interface　enhancement　effect＇　between　the　fibers　and　matrix　results　in　a　relatively　smooth　fracture　morphology.　At　the　macroscopic　level,　morphology　evolution　reflects　the　transition　from　brittle　to　pseudo-plastic　behavior.　Additionally,　based　on　the　principle　of　minimum　potential　energy　and　the　theory　of　semi-geodesics,　the　complex　macroscopic　structure　and　microscopic　Representative　Volume　Element　(RVE)　model　was　reconstructed.　The　findings　show　the　numerical　model　accurately　represents　the　circumferential　damage　of　SiCf/SiC　CMC　under　extreme　temperatures.　Simultaneously,　at　the　molecular　level,　the　interfacial　strength　at　high　temperature　is　7.5　%　higher　than　that　at　ordinary　temperature,　resulting　in　a　distinct　adhesive　interaction　between　matrix　and　fibers.　This　study　opens　up　new　avenues　for　the　fundamental　theoretical　research　of　such　ceramic　matrix　materials.　interface　enhancement　effect.　©　2024　Elsevier　Ltd　and　Techna　Group　S.r.l.