Due to its excellent performance, SiCp/Al composites have been widely used in high-tech fields such as aerospace, optical, and automotive industries. However, the gap between plasticity and hardness is huge, making ultra-precision machining very difficult.The ultrasonic milling dynamics model was established. The surface roughness and surface topography of SiCp/Al composites under different spindle speeds, milling speeds and milling depths were analyzed by single factor method.The tool milling trajectory of the longitudinal torsional composite ultrasonic vibration was modeled and simulated.The law and mechanism influencing the surface quality were obtained. It is found that when the spindle speed is 3 000 r/min and the milling speed is 180 m/min, the surface roughness value is the smallest; the surface quality of the material decreases with the increase of the milling depth. It provides reasonable process parameters for milling of SiCp/Al composites, machining efficiency is improved, tool wear is reduced and tool life is prolonged.