ZrC nano-particles with varied mass fractions were introduced into the CFRP (carbon fiber-reinforced plastics) green body by a slurry infiltration technique. After the pyrolysis of CFRP green body, the C/C-ZrC preform with different microstructure features were obtained. By infiltrating the liquid silicon into the C/C-ZrC preform, the C/C-SiC-ZrC composites were successfully fabricated. The morphologies of C/C-ZrC perform and C/C-SiC-ZrC were observed by scanning electron microscopy (SEM). The porosity was measured by using the Archimedes method. The mechanical properties were evaluated by means of three point bending and single edge notched-beam (SENB) tests, respectively. The morphologies of C/C-ZrC perform show that the ZrC nano-particles distributed homogeneously in the fiber bundle area and had a obvious influence on the microstructure. The measurement of mechanical properties found that the C/C-SiC-ZrC composites with a mass fraction of 5% nano-particles presented the highest value in the flexural strength and fractural toughness. While the mass fraction of nano-particles exceeds the 5%, both the flexural strength and fracture toughness of composites decreased. Combing the mechanical properties with the microstructure analysis, the high mechanical properties could be attributed to the more homogeneous distribution of SiC phase and the moderate fiber/matrix interfacial bonding strength.