This research integrated Grey Relational Analysis and Response Surface Methodology with D2MAIC. Users can select critical parameters to optimize process with data calculation and reduce the percentage of human error. In order to verify this model, this research took a CNC experiment and defined the surface roughness value as the index of quality. It looks forward to reducing the surface roughness value. According to the result, the surface roughness value has improved 50%. The result has confirmed the feasibility.