C/C composites have a wide range of applications in aerospace materials due to their low density, high temperature resistance and other characteristics. Improving the microwave absorbing performance of these materials through modification methods is expected to broaden their application fields. In this paper, C/C composite, SiC nanowire (SiCnw), and SiCnw modified C/C composite were fabricated by precursor infiltration and pyrolysis method, and chemical vapor reaction method using phenolic resin, Si, SiO2 and catalyst ferrocene as raw materials. The microstructures and properties of C/C and SiCnw/C/C composites were studied, and the influence of SiCnw content to electromagnetic wave absorption performance of C/C composites was discussed. The results show that SiCnw with core/shell structure is successfully introduced into C/C composite, and the SiCnw/C/C composite exhibits excellent electromagnetic wave absorption performance with the increasing of SiCnw content, and the minimum reflection loss of SiCnw/C/C composite with 15.4% (mass fraction) SiCnw is -38.02 dB with a thickness of 2.07 mm, significantly lower than those of other materials. This work provides a technical and theoretical basis for the preparation of high-performance carbon/ceramic composites.