Abstract: Using 2.5D fabric/mat layered needled preforms as reinforcements, two types of C/C preforms with densities of （1.35±0.02）g/cm³ and （1.50±0.02） g/cm³ were prepared, and then C/C-SiC composites were fabricated via reactive melt infiltration. Ablation tests were conducted on the prepared composites under oxyacetylene and supersonic oxygen-enriched ablation environments to investigate the effect of C/C preform density on the microstructure and ablation performance of needled C/C-SiC materials, and the ablation mechanism was analyzed. The results show that the surface of the needled C/C-SiC spherical head prepared by reactive melt infiltration forms a SiC-enriched layer, while a continuous SiC phase network forms inside; the C/C preform density does not change the overall structure of the SiC continuous network, but the material prepared from the low-density C/C preform exhibits better connectivity, lower porosity, and higher SiC content. The C/C-SiC spherical heads prepared from C/C preforms of different densities exhibit comparable ablation resistance under the oxyacetylene environment, with an ablation rate of 4.6×10⁻³~5.1×10⁻³ mm/s. However, under the supersonic oxygen-enriched ablation environment, the spherical head sample prepared from the low-density C/C preform shows better ablation resistance, with a linear ablation rate of 3.1×10⁻³ mm/s. This is mainly attributed to the higher SiC content in the C/C-SiC composites prepared from the low-density C/C preform, which can continuously oxidize to generate sufficient SiO₂ to effectively protect the fibers, thereby reducing the ablation rate.