Abstract: C/C composites were prepared by resin infiltration and pyrolysis with 3D needle-punched carbon fiber preforms. The reactive melt infiltration process was used subsequently to prepare C/SiC composites，and the liquid Si or Si-Mo alloy was used as the reactive melt. The microstructure evolution during the preparation process of C/C composites was investigated. The results indicate that resin mainly exists in the small pores of the fiber bundles. Pores become more and bigger but there are dense C/C segments within the fiber bundles after pyrolysis. High temperature treatment leads to a higher graphitization degree and makes the closed pores open，which acts as the channel for silicon infiltration. Some fibers inside the fiber bundles of C/SiC composite infiltrated by Si are damaged and much residual Si exists in big pores. When C/SiC composites are fabricated by Si-Mo infiltration，the remaining Si content is reduced，the damage of fibers inside the fiber bundles is much slighter and the C/C segments remain intact.