Abstract: The statistical analysis of in-situ fiber bundle failure was examined for 3D C/C composites by different processing technology. An in-situ interfacial strength testing instrument was used to determine the fiber/matrix bond properties of C/C composites. This paper also introduces a micromechanics model for the study of the stress and strain fields along the fiber/matrix interface and provides a description method of the interface properties by the debonding force and mechanical properties of fiber,matrix and composites. The analysis shows that the results can provide an optimal design of C/C composites. Associated with high temperature processing are the phenomena of fiber bundle strength loss up to about 20%.Comparing the different interfaces reveals that fiber bundles in the z direction have the best bonding and the strongest interphase.