Abstract: The surface morphology, surface roughness, residual stress, hardness and fatigue properties of 2A12-T4 aluminum alloy samples processed by diamond tool and carbide tool mirror milling and chemical milling were studied by contrast. The results show that comparing with that of chemical milled samples, the detailed fatigue rated strength of carbide tool mirror milled equal thickness flat sample (one side for carbide tool processing and the other side for diamond tool processing) was improved by 4.27%, while that of diamond tool mirror milled depression sample was improved by 22.46%. The fatigue resistance of diamond tool mirror milled sample was higher than that of carbide tool mirror milled and chemical milled samples. The diamond tool mirror milling introduced residual compressive stress on the sample surface, improved the surface hardness, decreased the surface roughness, and did not damage the surface structure, resulting in increase of crack initiation and propagation resistance. The pits, intergranular corrosion defect and residual tensile stress on chemical milled sample surface, and deep tool grooving and residual tensile stress on carbide tool mirror milled sample surface all promoted the initiation of cracks.