The modified C/C composite was quickly prepared by the approach of liquid impregnation combined with reactive melt infiltration. The microstructure was studied and the ablation behavior exposed under oxyacetylene flame and highfrequency plasma wind tunnel atmosphere was assessed. Results show that many high melting point refractory compounds such as HfC, ZrC, TaC are introduced into the modified C/C composite, the density and open porosity of which are 3.83 g/cm³ and 4.71%, respectively. A compact oxide film generates upon the modified C/C composite after oxyacetylene flame ablated 360 s, which is mainly composed of HfO₂, ZrO₂ and Ta₂O₅. The linear ablation rate of modified C/C composite is 0.005 18 mm/s. The ablation resistance of modified C/C composite bulb model is assessed by high-frequency plasma wind tunnel, the heat flux is 3.53 MW/m², the stagnation temperature is 2293 ℃, and the test duration is 180s. After ablation, a dense oxide protective layer forms on the surface of the model, the shape and the dimension of the model are changed insignificantly, and the linear ablation rate is 0.001 72 mm/s after removing the oxide layer.