Abstract: In recent years, according to the development trend of material adding and subtracting technology, it is necessary to realize the material adding and subtracting function on the same CNC machine tool. A set of composite ram structure is designed to realize the efficient combination and integration of the 3D printing head and the machining head. The forming function of the workpiece is realized through the additive function of 3D printing technology, and then the designated part is processed through the machining technology, thus realizing the one-stop forming and processing function of the predetermined workpiece. This structural design has been verified by practical application on a gantry machine tool with compound functions of adding and subtracting materials, which greatly reduces the handling of workpieces in the production process and avoids the workpiece clamping deviation caused by multiple positioning and clamping. The results show that the structural design is reasonable, especially for machine tools with large and medium-sized components. This structure greatly simplifies the structural complexity of the equipment, reduces the direct material investment of the equipment, but also increases the overall reliability, efficiency and price-performance ratio of the products.