In order to improve the quality and control precision of the end surface of the hole, the optimization of the processing parameters of the laser modified grinding hole of the hard material is tested and studied under the assistance of the ultrasonic vibration. By using the rotary ultrasonic method, the processing efficiency is significantly improved, and the difficulty of processing hard and brittle material holes is effectively overcome. In order to judge the quality level (Hd value) of the hole outlet, the range of the collapse area is analyzed, and the area ratio of the hole section is measured, and further discusses the influence of laser modified grinding process parameters on Hd value. Through the comprehensive test analysis, the best laser modified grinding process parameters are determined: the spindle speed is 14000–16000 r/min, the feed speed is 0.5–0.7 mm/min, and the amplitude is 7–8 μm. Compared with the traditional laser processing, the surface finish after ultrasound-assisted laser modification under the optimal parameters is significantly improved, and the scratches are greatly reduced, which significantly improves the processing quality. This study has important guiding significance for improving the quality of laser modified grinding of hard materials, and it can be easily applied in practical production.