SiO₂ fiber reinforced polyimide composites were heterogeneous anisotropic materials,the processing properties were highly dependent on the fiber orientation angle which is between the direction of fiber layers and the direction of processing feed.In this paper,the effects of fiber orientation angle on surface morphology,surface roughness,milling force and tool wear were studied through a series of experiments of dry cutting and ultra-low temperature cooling milling with different fiber orientation angles.The results show that the types of shear stress and styles of cutting chips are different under different fiber orientation angles.The milling surface roughness is fine when the fiber orientation angle is acute.When the fiber orientation angle increases to 90°,the cutting surface quality decreases and the cutting force increases.In the same milling time, the tool wear is serious in dry cutting,and the falling off area of coating is about 70% of the measured area. But compared to dry cutting,in ultra-low temperature cooling milling,the coating is not seriously damaged,the tool is still in a stable wear stage, and the tool durability is better than that under dry cutting condition.