By using polycarbosilane as precursor and SiC whisker，SiC powder or carbon fiber as reinforcer，the SiC/SiC or C/SiC composite was fabricated. The influences of the properties of mechanics and thermal physics were investigated. The results showed that at 1300℃ polycarbosilane was transformed into β-SiC mic-crystal which linked the reinforcer to form the SiC/SiC or C/SiC composite. The composite has good mechanical properties at both room temperature and high temperature，excellent thermal shock resistance and thermal fatigur resistance，and good oxidation resistance at 1300℃ in air.