Tensile properties and fracture mechanisms of SiCf/TC17 composites at room temperature and 773 K were studied. The results show that fiber elastic deformation and matrix yielding contributed to the shapes of the stress-strain curves of SiCf/TC17 composites, which were the bilinear appearance at 298 K and the slight curvature at 773 K. Major fracture mechanism of SiCf/TC17 composites at room temperature were as follows: multiple fractures of the interfacial reaction layer, single fiber fracture, matrix brittle fracture etc.. Typical fracture mechanism of SiCf/TC17 composites at elevated temperature were as follows: multiple fiber fracture, matrix plastic fracture, interface debonding etc.. Fiber cumulating damage theory was proved to be suitable for estimation of the fracture strength of this composite. The calculations of local loading sharing model while taking three or more fibers failure into account and global loading sharing model were close to the experimental values of room temperature and elevated temperature respectively. In addition, according to fracture mechanisms and strength prediction, tensile fracture process of SiCf/TC17 composites at room and elevated temperature were explained in detail. At room temperature, multiple fractures of the interfacial reaction layer started at first, and then the weak fiber fractured gradually and randomly. After critical fiber cluster has been formed by nearby broken fibers, the crack extended into the matrix from these fibers. With the increase of load, the fibers and the matrix at the tip of crack gradually destroyed. At the same time, the cracks from other critical fiber clusters were also expanding and connecting to each other. When the crack area has reached the critical level, the remaining fiber and matrix quickly fractured. However, at elevated temperature the matrix yielded firstly, and then multiple fracture randomly of the interfacial reaction layer and the weak fiber occurred sequentially. The crack from broken fiber deflected at interface between fiber and matrix, caused interface debonding. With the increasing of broken fiber number, the micro-cavities of matrix emerged gradually in the stress concentration area. When the total crack area accumulated by the broken fibers and micro-cavities of matrix has reached the critical level, the remaining fiber and matrix quickly fractured.