In order to explore the change law of the cutting force and surface roughness of 45%SiCp/Al composites, the turning orthogonal test of 45%SiCp/Al composites and aluminum alloy materials was carried out with PCD tool.The influence law of particle content and cutting speed on the cutting force and the force fluctuation was analyzed, as well as the influence of force fluctuation on surface roughness.The results show that for 45%SiCp/Al composites and aluminum alloy materials, the higher the particle content, the larger the threedirection cutting forces such as Fx, Fy and Fz,and the smaller the force fluctuation.In the cutting process of 45%SiCp/Al composites, the feed force is less than the back force and the main cutting force in general,but when the cutting speed is in 90~120 m/min, the back force is greater than the main cutting force; when the cutting speed increases, the cutting force and the fluctuation value of the force tend to increase first and then decrease and increase finally; the larger the variation range of cutting force fluctuation, the larger the surface roughness