Ultra-precision raster milling induces external stress to cause phase changes of Zn–Al alloy at a thin surface layer, which further degrade surface integrity of high-precision components. This study focuses on discussing phase changes at the surfaces of the alloy after ultra-precision raster milling under the high cutting speeds of 680 m/min, 1120 m/min, and 1360 m/min. Along with the penetration depth at the machined surfaces, phase changes and surface hardening rapidly declined to vanish with crystal orientation shift back to its standard Bragg angle. As the cutting speeds increased, phase changes, crystal orientation shift, and surface hardening obviously decreased with phase change thicknesses from 323 nm, 241 nm to 87 nm. It is worth noticing that at a high cutting speed phase changes at the machined surface can be greatly reduced to a significant degree.