Abstract: The interfacial performances of carbon/carbon composites in different process stages were characterized by push-out method to find the formation law of fiber-bundle/matrix interlayer in the process of carbon/carbon composites preparation. Microstructures in fiber-bundle/matrix interlayer of carbon/carbon composites obtained from different process stages were investigated through SEM, Micro-CT, XRD and Raman spectrum. Experiment results of interfacial shear strength of specimens obtained from different process stages show that, the interfacial shear strength of specimen with lower density was not clearly increased with the degree of graphitization increasing; however, the interfacial shear strength was clearly increased with the density of specimens increasing. The observation of the interfacial microstructures of the composite showed that matrix was firstly formed in intrabundles, then formed in bundle surface and interbundles. The degrees of graphitization and crystallization at surface were gradually increased with heat-treatment temperature increasing. The experiment results show that interfacial structures and performances in fiber-bundle/matrix interlayer of carbon/carbon composites gradually develop to be perfect with repeated cycles of in-ltration-carbonization-graphitization process.