BN/SiC coatings were deposited on the surface of SiC fibers by chemical vapor infiltration (CVI) process, and the physicochemical properties of the surface coatings and the fibers were further investigated by characterization techniques in a high-temperature oxidation environment. The fibers coated with BN/SiC coatings were treated at 1050 – 1200 ℃ for 0.5 – 2 h in air environment. The morphology, structure and composition of the oxidized BN/SiC coatings were characterized by scanning electron microscopy (SEM), X-ray diffractometer (XRD), nano-scanning Auger (AES) and X-ray photoelectron spectroscopy (XPS). The mechanical properties of SiC fibers coated with BN/SiC coatings after oxidation were evaluated by tensile strength of monofilament. The results show that the BN/SiC coatings are not completely oxidized and still have the ability to protect the internal SiC fibers. Through further analysis of the experimental data, it is found that the main failure mechanisms of the fibers attached to the coatings after oxidation at 1200 ℃ and 1350 ℃ are different, with the former being the formation of gaps and pores between the coatings and fibers, and the latter being the production of oxides and their cracks.