Abstract: In this paper, the method of manufacturing FDM thin-walled parts by adding and subtracting materials is studied. The traditional independent double nozzle 3D printer is reformed by combining additive manufacturing and material reduction manufacturing. The right nozzle is modified as NC milling cutter. When 3D printing model slices, the contour of the model is identified and processed to generate NC machining code, which is automatically integrated into 3D printing G code. The thin-walled parts can be directly printed and high-precision surface quality can be obtained. For the processing of thin-walled and complex structure plastic parts, the G code of composite processing can be generated automatically by the modified additive printer, which greatly improves the efficiency of additive and additive composite manufacturing.