We proposed a new processing method to reduce the cutting force of the machining process effectively, as well as to improve tool life and machining process efficiency. The proposed method, called the milling–milling machining method, is a new form of composite machining that is similar to the turn-milling method. It combines the advantages of face milling and helical end-milling cutters and uses the synthesis motion of these kinds of cutters to complete surface processing. This technique effectively reduces cutting force and, thus, improves tool life and machining efficiency. The milling–milling machining method has the advantages of a large diameter face mill with a large milling area, a low cutting force, a stable and highly efficient cutting process that is similar to that of a helical end-milling cutter, and trochoidal milling. The outstanding characteristics of face milling and helical end-milling cutters can be applied directly to the milling–milling machining method. In addition, the proposed method has unique features. The up–down milling–milling machining method can offset a portion of the cutting forces. Apart from proposing the theory for the milling–milling machining method, we also designed new equipment, namely the planetary cutter, milling–milling driving head, and a computer numerically controlled milling–milling machine. We compared the proposed method and the common face milling method from the perspective of cutting forces. Experimental results show that the milling–milling machining method considerably reduces cutting forces compared with conventional methods.