The carbon fiber–reinforced plastics have gained considerable attention in the aerospace industry in recent years. Drilling of carbon fiber–reinforced plastic is relatively difficult with too much fiber delamination and pulling out in the entry and exit of the holes. As an advanced hole-making technology, helical milling is being developed in machining of carbon fiber–reinforced plastic, in which the tool moves on a helical course to the workpiece. Experiments were carried out on helical milling of carbon fiber–reinforced plastic, the effects of the cutting parameters and tool wear on the cutting forces are analyzed, and the relation between hole quality and cutting forces is also discussed. In order to simulate the cutting forces under different cutting conditions, the mechanistic modeling technique is used to predict cutting forces in helical milling of carbon fiber–reinforced plastic, and the cutting force coefficients are identified and corrected based on the experimental data. The results show that the established model can be used to predict the cutting forces in the helical milling process.