To improve the surface quality of the exit edges of C/C composite holes, the value of the hole exit damage factor S_d (the ratio of the damaged area of the hole exit face to the ideal hole area after machining) is used as an indicator of hole exit quality. The grinding process parameters were optimized using single-factor and orthogonal test methods to analyse the hole exit edge grinding mechanism and propose a hole damage suppression strategy. The results show that when the spindle speed is 12000–14000 r/min, feed rate 5–7 mm/min, and ultrasonic amplitude 8–9 μm, the S_d value could be within 4.723×10^–3. The S_d value can be further reduced by 61.6% using the hole damage suppression strategy. Moreover, the S_d value of C/C composites under ultrasound-assisted grinding decreases and then increases with the increase of spindle speed and ultrasonic amplitude while gradually increases with increasing feed speed. When the optimum feed speed is ensured, increasing the spindle speed and ultrasonic amplitude will help to improve the surface quality of the hole exit and increase machining efficiency. The strategies of reducing the feed speed near the hole exit, using the side wall of the tool to smoothly grind the hole exit and adding an auxiliary support under the workpiece are effective in reducing hole exit damage.