Optical glass is the key material for manufacturing optical devices such as lenses and filter mirrors. Owing to its high hardness, high brittleness and low fracture toughness, edge damage has been the major defect during the machining of optical glass. Based on the drilling experiment of BK7 optical glass, the damage characteristics at the entrance and exit of the machined hole were analyzed; subsequently, the formation mechanism of edge damage was discussed by using the compression fracture theory of brittle materials; and finally, the influence of drilling parameters was studied. Consequently, the suppression effect of Rotary Ultrasonic Drilling (RUD) and Rotary Ultrasonic Pecking Drilling (RUPD) on edge damage was studied. The results indicate that ‘local edge chipping’ is the main form of the entrance damage, and the superposition of ‘layer separation’ and ‘discontinuous chipping’ is the main character of the exit damage. The subsurface lateral crack expansion, caused by squeezing the tool end abrasive, is the main cause of generating entrance damage, whereas the middle crack expansion and axial collapse are the main causes of exit damage. The RUD has a clear effect on the reduction of hole edge damage: its maximum entrance chipping size Lin_max and the maximum exit separation size can be decreased by 15%—50% and 45%—65% of common drilling, respectively. The RUPD can promote the expulsion of abrasive scraps; thus, achieving less exit damage than the RUD.