A grinding experiment was performed for silicon carbide (SiC) materials by Ultrasonic Assisted Grinding (UAG) and Normal Grinding (CG) methods. The effects of grinding parameters in different modes on the grinding force ratio, surface damage and sub-surface damage of the SiC materials were researched by using a dynamometer and a Scanning Electron Microscopy(SEM). Then the action mechanism of the UAG was researched. The experimental results show that brittle fracture is the main removal mode in grinding process. The grinding force ratio of the grinding wheel increases with the increases of cutting depth and feed rates slowly and decreases with the increase of pindle speed slightly. In the normal grinding, the sub-surface damage depth of a SiC workpiece increases with the increase of cutting depth and feed rates gradually, and that in the UAG has a smaller change. Under the same grinding parameters, the grinding force ratio in UAG process is reduced nearly 1/3 as compared with the results in CG process, and its surface damages, such as surface cracks, fall off of SiC grains, flaking of SiC are reduced and the thickness of surface damage layer is thinned. In addition, the density and depths of sub-surface cracks are reduced in a greater degree. It concludes that the UAG method can obtain ideal surface quality and high processing efficiency.