The fluctuations of cutting force may result in unstable machining processes when the thinwall parts are machined. So cutting process needs to be optimized. An optimized model of NC programming for milling of Inconel 718 thinwall parts was established. The presented model consists of NC programming, material database and CNC machining simulation. The solid module of workpiece was developed with UG software and NC codes were programmed. The parameters of cutting force and temperature for Inconel 718 were simulated by finite element method using AdvantEdge FEM based on the Power Law constitutive equation. The effects of the workpiece material properties and material separation criterion on cutting force and cutting temperature were analyzed. The model of workblank, NC codes and materials were input into Production Module to optimize the cutting process. The result shows that the proposed method of optimization model of NC programming can diminish the fluctuation of cutting force, which will be beneficial to improve the stability of thinwall parts machining.