Abstract: Aiming at the problems that large complex thin-walled shell is easy to deform and the machining precision is difficult to meet the requirements, the NC machining technology is studied. Take the tail section of a carrier rocket as an example, in order to effectively control the machining deformation and guarantee the accuracy of the product. The structural characteristics of the workpiece and the main factors affecting the machining deformation are analyzed, targeted to develop a reasonable NC machining process scheme, including reasonable arrangement of machining process, the use of appropriate stress reduction and aging methods, optimization of clamping scheme and reasonable planning of tool path, to achieve the deformation of the workpiece control and effective clamping, to ensure the finished workpiece precision requirements. Finally, the correctness and effectiveness of the process plan are verified by the actual processing application.