Abstract: The milling machining process of carbon fiber reinforced plastic (CFRP) could generate undesirable defects such as delamination and burr under the cutting forces, due to low bonding strength between the layers.Therefore, the prediction and control of cutting forces can substantially improve the machining quality.The milling forces in side milling multi-layer CFRP with multitooth cutter were modeled and simulated by using an instantaneous rigid force model.And the influence of special tool geometry of multitooth cutter on milling forces was analyzed.Milling tests of unidirectional CFRP in typical directions (45°, 0°, -45°, 90°) were carried out at the same cutting speed but with different feed speeds.Thus milling force coefficients of each unidirectional CFRP were also calculated by the test data of cutting force.Based on vector superposition principle, the simplified expression for milling force coefficients of multi-directional CFRP was obtained.Finally, the caculated results were substituted into milling forces model and the simulated value of milling force at each moment were obtained.Furthermore, verification test of milling multi-directional CFRP was carried out under the same machining condition.The results show that the model can well predict the milling force that the maximum relative error is less than 9% and average relative error is less than 5%.Thus, the model can provide a theoretical basis for cutting parameter optimization and tool geometry optimization.