CFRP (carbon fiber reinforced plastic) is widely used in aerospace field because of its excellent mechanical properties. Under the premise of ensuring the stiffness and strength of the aircraft, the application of CFRP can effectively improve the flight performance and reduce the weight of the aircraft, so as to achieve the purpose of energy saving and emission reduction, and improve the economic benefits of the aviation industry. CFRP is a typical difficultto-machining material, and in order to ensure that the structure has load-bearing capacity in different directions, CFRP multidirectional lamination is generally used in the aero-engine industry, which makes the anisotropy and inhomogeneity of the material more complex. In this paper, the milling fracture mechanism of CFRP unidirectional laminates and two kinds of CFRP multidirectional laminates is analyzed, and it is found that different fiber direction angles have great influence on the fracture mechanism during CFRP milling, resulting in different surface quality. Among them, bending fracture will lead to a sharp decline in surface quality, which should be avoided as far as possible, and the surface quality of bending fracture at different angles is also different. Based on this, an optimization method of tool cut-in angle in multidirectional CFRP milling is proposed, and the rationality of this method is verified by experiments. This method can effectively improve the machining quality of the first-stage composite fan blade of a certain engine.