To investigate the interactive effects of micro-cracks on the surfaces and subsurfaces of BK7 optical glass materials during ultrasonic vibration assisted grinding, a group of twice-indentation experiments using Vickers diamond indenters were conducted on BK7 optical glass to simulate the multi-indention effect of single abrasive grit on optical glass under ultrasonic vibration. In addition, the bonded interface technique was performed on the specimens to determine the morphologies of the indentations and micro-cracks on the surface and subsurface of the optical glass. The experimental results show that the maximum depth of subsurface cracks produced by the second indentation is affected by the previous lateral cracks and is reduced by 30 μm under the same loading conditions. Furthermore, the optical glass materials will be broken after lateral crack are closed on the surface or inside of the optical glass. Based on indentation fracture mechanics, a model of elastic/plastic stress fields in the BK7 optical glass under indention loading was established to analyze the mechanism of micro-cracks propagation and the shield effect. The analysis of the interaction of micro-cracks as influenced by ultrasonic vibration reveals that the depth of subsurface cracks decreases and the material removal efficiency is improved with ultrasonic vibration assistance.