Abstract: Nano silicon carbide composites reinforced by carbon fibers have excellent mechanical property and biocompatibility，and can be used as a full scale human skeleton to take the place of   titanium alloy. The purpose of this paper is to investigate the effects of 3D orthogonal plaiting textures of T300 and M30 carbon fibers on the preparation process and flexural strength. C/SiC composites were prepared by polymer infiltration pyrolysis using polycarbosilane as preceramic and divinylbenzene as solvent. The density and porosity of C/SiC composites were measured by the Archimedes method. The flexural strength was tested by the method of  three points bending. The flexural strength of M30 C/SiC composites is about 6.7% greater than that of T300 C/SiC composites. The results indicate that the cracking strength of C/SiC composites is dramatically affected by the elastic modulus of carbon fibers. High flexural strength of M30 C/SiC composites resulted from the high radial strength and high load bearing ratio of fiber to matrix，which all resulted from the higher elastic modulus of M30 than that of T300 carbon fibers.