Abstract: 2D-C/C composites were prepared by pyrocarbon deposition at 1000－1100℃ using liquefied petroleum gas as the carbon source and a 2D carbon fiber weave as substrate. Graphitized samples were obtained by heat treatment at 2800℃ for 10h. An engine torch test was used to evaluate the ablation properties of the two kinds of composites. A comparison of the pore size distribution, the cohesion strength between matrix and fiber, and the thermal conductivity of the two composites was used to explain their ablation characteristics and mechanism. Results show that for the 2D-C/C composites, the ablation mechanism is controlled by a thermo-chemical reaction (oxidation), the ablated surface is even and the ablation rate is 0.033mm/s because of its low porosity, large cohesion strength and low out-of-plane thermal conductivity. For the graphitized 2D-C/C composites, the ablation mechanism is dominated by both oxidation and mechanical wearing with a few macroscopic pits on the ablated surface and the ablation rate is 0.046mm/s, which is caused by their large porosity and low cohesion strength.