Abstract: In order to reduce the content of residual Si generated in the process of liquid silicon infiltration, B₁₂(C, Si, B)₃ modified C/C-SiC composite was prepared by a joint process of slurry impregnation and liquid silicon infiltration. By analyzing the products of B₄C-Si system with different B₄C/Si molar ratios after sintered at different temperatures, the formation condition of B₁₂(C, Si, B)₃ was studied. The results indicate that B₄C starts to react with Si at 1300℃, leading to the formation of a small amount of B₁₂(C, Si, B)₃ and SiC. The amount of B₁₂(C, Si, B)₃ generated in the reaction increases with increasing sintering temperature. The sintering product of B₄C-Si system with a B₄C/Si molar ratio of 3:1 at 1500℃ is composed of B₁₂ (C, Si, B)₃ and SiC. The C/C-SiC composite fabricated by liquid silicon infiltration is composed of amorphous C, β-SiC and B₁₂(C,Si,B)₃, and no residual Si is detected.