In this paper, C/ SiC composites were machined by traditional grinding and ultrasonic vibration-assisted grinding. Surface characterizations and mechanical properties of the C/ SiC composites grinded under different processing parameters are measured. Results of performance test indicated that the composite material machined by ultrasonic assisted grinding process obtained the better surface roughness quality and the greater bending strength,the best processing parameters were: grinding depth 0. 05 mm, feed velocity 600 mm/ h, speed 1 600 r/ min, ultrasonic frequency 14 kHz. It shows that ultrasonic vibration-assisted grinding has the lower damage to material mechanical properties.