In the present work, ultrasonic assisted grinding (UAG) and conventional grinding (CG, without ultrasonic) tests of Carbon fiber reinforced silicon carbide matrix (C/SiC) composites were conducted. In addition, analysis was done by comparing the machining quality, grinding force, and specific grinding energy between the two processes. The results showed that material removal mode of carbon fiber both in CG and UAG were brittle fracture, and fracture size had no obvious difference. Compared with CG, brittle fracture area of SiC increased during UAG. In comparison with CG, the normal grinding force and tangential grinding force for UAG were reduced maximally by 45%, 39% respectively of those for CG. Accordingly, specific grinding energy was also reduced by UAG. Therefore, UAG can improve the grinding performance of C/SiC composites significantly.