This paper aims to study the machinability of carbon fiber reinforced Mg-matrix composite (C_f/Mg), the ultrasonic assisted cutting experiments of carbide milling cutters and carbide drill bits are carried out. Through orthogonal test, it is found that the milling force of ultrasound-assisted milling Cf/Mg composite increases with the increase of feed and milling depth of each tooth, and decreases with the increase of spindle speed. In the test, when ultrasonic assisted milling is carried out, the feed per tooth is 0.025mm, the milling depth is 0.2mm, and the milling force is the minimum under the processing parameters of 6000r/min. The feed per tooth is 0.025mm, the milling depth is 0.2mm, and the surface quality under the processing parameters of 4000r/min is relatively good. When single factor drilling test is carried out with carbide bit, the axial drilling force decreases with the increase of spindle speed. Compared with traditional drilling, ultrasonic assisted drilling can reduce the axial drilling force. Compared with traditional drilling, ultrasonic assisted drilling can reduce the axial drilling force by about 36% when the machine speed is 6000r/min and the feed speed of the machine is 100mm/min. Compared with traditional drilling, ultrasonic assisted drilling can decrease burr and stratification at the drilling exit.