Abstract: The fatigue property of T700/HT280 composite and HT280 resin in high temperature environment were studied via the stiffness reduction theory.The mass loss rate of composite and resin was measured.The chemical construction,interior damage and dynamic mechanical behavior were analyzed by FTIR,ultrasonic C-scanning and DMA.The results indicate that the mass loss rate T700/HT280 composite and HT280 resin increases rapidly at the initial aging stage and then increases slowly with further aging.After the long-term exposure to high temperature,thermal-oxidative aging can be seen in HT280 resin.The change of dynamic mechanical properties of HT280 resin is attributed to the post-curing and thermal aging,while for T700/HT280 composite,it is attributed to the synthetic action of the post-curing,thermal aging and interface debonding.The stiffness decline rate of treated composite is less than the original one.It indicates that the strengthening effect of post-curing and thermal aging is obvious after exposuring to high temperature.Therefore,a certain improvement in the fatigue-resistance of T700/HT280 composite can be obtained.