The interfacial properties such as debond strength, fracture energy release rate in Mode-II and coefficient of friction play important roles in determining the mechanical properties and strength of carbon/carbon (C/C) composites. Push-out tests were conducted on 3D C/C composites and the experimental results were fitted to the shear lag model to determine these interfacial properties. X-ray tomography was used to explore the internal material structure of the composite. The fiber bundle and matrix interfaces were observed as being partially damaged in the tomographic images and the crack network was explored in detail. The tomographic images were also used to reconstruct a finite element (FE) mesh for simulating push-out tests. The interface of the fiber bundle and matrix in the FE mesh was represented by cohesive surfaces with frictional contact. The cohesive surface properties were obtained by matching FE results with the experimental results. The simulations had a good agreement with experiments and values of 0.75 for coefficient of friction, 2–5 N/mm2 for debond stress, 1–4 N/mm2 for clamping stress and 3–6 N/m for fracture energy release rate were obtained as interfacial parameters for the composite.