Abstract: During the milling process of quartz fiber-reinforced ceramic matrix composites, defects such as fiber debonding, matrix fragmentation, and pits are extremely prone to occur. To improve the machinability, the material removal mechanism under ultrasonic vibration assistance was analyzed, and the effects of processing parameters on milling forces, temperature, and surface quality in both conventional milling (CM) and ultrasound vibration-assisted milling (UM) were investigated. Compared with conventional milling, the milling forces in the vertical feed direction and parallel feed direction were reduced by up to 38.41% and 29.93%, respectively, and the milling temperature was decreased by a maximum of 23.51%. In addition, the surface roughness of ultrasonic vibration-assisted milling was reduced by 51.12% compared with conventional milling, and the occurrence of surface defects such as fiber fracture and matrix fragmentation was reduced. When machining quartz fiber-reinforced ceramic matrix composites, ultrasonic vibration-assisted milling can effectively reduce milling forces and temperature and significantly improve the machined surface quality by reducing cutting resistance and friction through high-frequency vibration.