The abrasive drilling achieves high hole qualities in processing carbon/epoxy (C/E) composites. In order to investigate the cutting force and the material removal mechanism for drilling C/E composites with abrasive drilling tool, this paper presented a mechanistic model to predict the cutting force of single grain. The model assumes fibers as a beam with two ends fixed. The beam is subjected to extrusion of diamond grain and mainly fractures by tensile damage. The failure mode is then validated by finite element simulation and scratching experiment. The cutting simulation of single grain using Abaqus showed fracture occurred in the points with maximum tensile stress. The tensile damage results in many claval chips. Local fiber tensile damage is the mainly failure mechanism for the fibers, accompanying the fiber compressive failure and shear failure.