Abstract: In order to study the influence of spindle speed on the surface roughness of the workpiece in contour milling machining, a machining inspection test system was built, the spindle speed was set as the variable, other experimental parameters were fixed, and four experiments were carried out at S=2000, 3000, 4000, and 5000 r/min, and the vibration of the workpiece was synchronously captured during the experiments. The experimental results show that with the increase of spindle speed, the cutting force during machining is reduced, the maximum amplitude and the average amplitude of the workpiece are decreased, the distance that the cutting edge slips on the surface of the workpiece is reduced, and the slip friction generated is small, thus reducing the surface roughness value and improving the surface quality. This conclusion can provide guiding experience for the selection of spindle speed in milling machining.