K9 glass has been widely used in modern hightech fields such as aerospace,automotive,optical precision instruments,electronic information,etc.due to its excellent performance,but its gap between plasticity and hardness is huge,making traditional mechanical processing prone to subsurface damage.Such phenomena,surface quality is difficult to meet the requirements.In this paper,the ultrasonic milling dynamics model is firstly established.Then the multifactor method is used to detect the longitudinal torsional composite ultrasonic milling and the ordinary milling K9 glass.The surface roughness and surface topography of different spindle speed,milling speed and milling depth are analyzed.Finally,the laws and mechanisms affecting the surface quality of the machine are obtained.It is found that the surface quality is best when the spindle speed is 3 000 r/min and the milling depth is 02 mm;the surface quality of K9 glass decreases with the increase of milling speed.The longitudinal torsional composite ultrasonic vibration milling improves the surface quality and processing efficiency of K9 glass,and provides the optimal process parameters for K9 glass longitudinal torsional ultrasonic milling.