Abstract: Ball head milling and flat bottom cutter milling have different cutting thermal performance, resulting in different machining residual stresses. In order to understand the residual stress characteristics of die steel surface by ball milling, ball milling tests were conducted for Cr12MoV . The influence of curved surface type, curvature, and sampling position on distribution of residual stress during machining was studied, and the residual stress of flat head milling plane was compared. The results indicate that the residual stress of mold steel curved surface machined by ball head milling is compressive stress. The shape and curvature radius of curved surface have an impact on the magnitude of residual stress. The shape of the curved surface changes in sequence of convex, flat, and concave, the absolute value of residual stress increases ; as the radius of convex curvature increases and the radius of concave curvature decreases, the absolute value of residual stress increases. When the surface curvature radius is same, the position has little effect on the residual stress, the residual stress changes very little.