The present article focuses on the change of mechanical properties of oxide fiber reinforced ceramic matrix composites with temperature from room temperature (RT) to 1400 ℃. Alumina fiber reinforced silica composite (Al₂O_3f /SiO₂) and quartz fiber reinforced silica composite (SiO_2f/SiO₂) were prepared by sol-gel process with alumina fiber and quartz fiber as reinforcement respectively. The tensile strength and compressive strength of the composites at room temperature ~1400 ℃ were investigated, and the microstructure and crystal phase structure of the composites were characterized by electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the mechanical properties of alumina fiber reinforced SiO₂ composites are much higher than those of quartz fiber reinforced SiO₂ composites under RT~1000 ℃. However, while the temperature was raised to 1200^℃, the mechanical properties decrease sharply, and strong bonding occurs between silica particles and fibers. As the temperature was further increased to 1300~1400 ℃, mullite and α-quartzite phases were formed. The mechanical properties of composites are sharply decreased due to brittle fracture under the action of stress. The brittle fracture caused by the disappearance of interfaces is the main mechanism of high temperature failure of composites.