Abstract: Based on the mesoscopic structure of the three-dimensional woven carbon/carbon (3D C/C) composite materials, a kind of flat cross-shaped specimen was designed followed by the test on biaxial mechanical testing machine under uniaxial and biaxial compression as well. Comparative analysis was carried out for the mechanical behavior of the 3D C/C composite materials under biaxial compression loading. The results show that the 3D C/C composite materials represent the non-linear compression behavior and brittle fracture. The nonlinear characteristics under biaxial loading are more significant, and the compression modulus increases along with the increase of stress. The strength and modulus of 3D C/C composites increase sharply under biaxial loading compared with the uniaxial results, and the enhanced effect of the material is remarkable. In addition, the fracture doesn’t appear in the central area of the specimen, but in the loading ends or the branch of the cross-shaped specimen. The main damages are matrix cracking, fiber breakage and interlaminar debonding. The compressive strength is affected directly by the carbon fiber cloth and the interlaminar shear strength of the material.