Unexpected work-piece deformation during the course of milling will lead to part bending or distorting, which is critical to get its quality performance lower. In this paper, a novel process based deformation control method is proposed using High Definition Metrology (HDM). Main factors that affect machining deformation of work-piece are analyzed firstly. Then process based deformation control model is made, which divides one machining process into four stages. The surface flatness data of work-piece at each stage are obtained respectively. Finally, the practicality and effectiveness of this new approach is verified using the case of Aluminum alloy 6061 part milling.