Because SiO₂ fiber reinforced polyimide composites are heterogeneous anisotropic materials,there are many serious issues in the traditional milling process,such as severe tool wear,large cutting force and low processing efficiency.In this paper,SiO₂ fiber reinforced polyimide composites are processed by cryogenic cooling milling.And the comparison between cryogenic cooling milling and traditional milling is also carried out.In addition,the machined surface morphology,roughness,cutting force and tool wear were analyzed.The results show that,the surface roughness decreases with the increase of spindle speed and decreases first and then increases with the increase of cutting depth under the two working conditions.Compared with traditional milling,cryogenic cooling milling at different cutting speeds can effectively inhibit the fiber fuzzing phenomenon during traditional milling with low-speed and the ablation defects of adhesives during conventional milling with high-speed. The main reasons for improving machining quality are the increase of cutting force,the change of fiber chip breaking mode and the decrease of cutting heat caused by ultra-low temperature cooling.