Abstract: A representative volume element model was proposed for C/C composites with the fibers oriented in four different directions. Three of the fiber directions were coplanar, at 120° to each other, and the fourth was perpendicular. The element truly reflects the orientations of the carbon fibers and matches the actual configuration of the composites. Based on the model and computational mesoscopic mechanics, the residual thermal stress distribution of the material at different graphitization temperatures, cooling rates, and interface stiffnesses was obtained using a finite element method. The residual thermal stresses of the composite from a low-graphitization temperature or with low interface stiffness are lower than those from a high-graphitization temperature or with high interface stiffness. The higher the cooling rate, the higher the residual thermal stress.