Abstract: In order to satisfy the urgent demand to test the mechanics/thermal/oxidization key performance parameters for new ultra-high temperature structures of hypersonic flight vehicles, a self-designed radiation type thermal-mechanical joint test system that can perform fracture property test of structures under extremely high-temperature/oxidization environment up to 1 500 ℃ was established. By using this system, key performance parameters, such as fracture strength and fracture time, for C/SiC high-temperature-resistant composite material were tested in high-temperature/oxidization environments up to 1 500 ℃. The results show that the C/SiC specimen's fracture load decreases 47.5% when the temperature rises from 1 000 ℃ to 1 500 ℃, and the time to failure reduces to 50.1% of that at 1 000 ℃. This extreme high-temperature experimental system provides important test method for thermal-mechanical research on thermal strength of structures in oxidization environments. In this thermal-mechanical test, the phenomenon that the preloading process in high temperatures can increase the fracture strength obviously for C/SiC composite structure is observed, and the fracture strength increases by 38% and the time to failure increases by 61.1%. The results provide important basis for the safety and reliability design as well as improvements of material strength properties of composite structures for hypersonic flight vehicles under extreme thermal environments.