<p>Carbon fiber reinforced polymer (CFRP) has gained considerable attention in the aerospace industry in recent years. To achieve reliable connections, the hole-making performance of CFRP must be systematically investigated. As a typical difficult-to-cut material, substantial tool wear will directly affect the variation of cutting forces in machining of CFRP. Excessive cutting forces, in turn, will induce the initiation and propagation of delamination around the holes. Thus, in this paper, the orthogonal cutting process of CFRP is simplified into three distinct deformation zones. Then, the cutting forces in each zone are analyzed separately. Considering the varying material removal mechanisms corresponding to different fiber orientation angles, the fracture characteristics of CFRP are investigated at the mesoscale to determine the orthogonal cutting forces. Based on oblique cutting theory and coordinate transformation, a preliminary three-dimensional cutting force model for the helical milling of CFRP is established. Furthermore, considering the variations in flank wear width of both the bottom and side cutting edges, a more reasonable theoretical model is developed. Finally, helical milling experiments on CFRP were conducted, and the effects of cutting parameters and tool wear on cutting forces were analyzed in detail. The results indicate that the proposed model can be used to predict the cutting forces in the helical milling of CFRP with reasonable accuracy.</p>