For the forming process of plate parts with local precision profile, the cutting-extruding compound trimming deflashing technology and its process were proposed and studied respectively，and the mechanics analysis of deformation zone was conducted. According to numerical simulation, the metal flowing mechanism was analyzed. The results show that metal deformation can be described by three deformation zones, such as the first, the second and the third deformation zone during the cutting-extruding compound trimming deflashing. The third deformation zone is the core of forming process, whose stress state directly affects the occurring of tear and quality of forming. The process of forming deformation can be divided into chip formation, stable forming and chip separation stage, among which the slippage is the most obvious in the stable forming stage. The compress stress produced by punch radius can limit the generation of fracture surface and improve the quality of forming surface.