This study is focused on a novel high-thermal-conductive C/C composite used in heat-redistribution thermal protection systems. The 3D mesophase pitch-based carbon fiber (CF_MP) preform was prepared using CF_MP in the X (Y) direction and polyacrylonitrile carbon fiber (CF_PAN) in the Z direction. After the preform was densified by chemical vapor infiltration (CVI) and polymer infiltration and pyrolysis (PIP), the 3D high-thermal-conductive C/C (C_MP/C) composite was obtained. The prepared C_MP/C composite has higher thermal conduction in the X and Y directions. After an ablation test, the CF_PAN becomes needle-shaped, while the CF_MP shows a wedge shape. The fiber/matrix and matrix/matrix interfaces are preferentially oxidized and damaged during ablation. After being coated by SiC coating, the thermal conductivity plays a significant role in decreasing the hot-side temperature and protecting the SiC coating from erosion by flame. The SiC-coated C_MP/C composite has better ablation resistance than the SiC-coated C_PAN/C composite. The mass ablation rate of the sample is 0.19 mg·(cm⁻²·s⁻¹), and the linear ablation rate is 0.52 μm·s⁻¹.