Abstract: Carbon fiber reinforced plastic(CFRP) are made up of fiber, resin and interface at the mesoscopic level. The essence of cutting process is a evolution process of material failure at mesoscopic level and chips formation at macro level. To reveal the mesoscopic failure of materials in cutting CFRP, a mesoscopic finite element model was built in cutting CFRP, which consists of fiber, matrix, interface constituent phases instead of using the traditional equivalent homogeneous modeling method. Different constituent phases not only based on their respective material constitutive, but also failure and evolution criterion were considered in order to simulate failure of materials. The processes of fiber/matrix fracture, interface break and evolution can be simulated actually from mesoscopic perspective in cutting process of CFRP unidirectional laminates of different fiber orientations. The simulation results show that the mesoscopic failure of CFRP materials differs at different fiber orientations. The destruction form at the fiber orientation of 0åre mainly interface cracking and fiber bending. At the fiber orientations of 45°/90°, fiber and matrix are crushed by cutting tool immersed in workpiece. At the fiber orientation of 135°, the destruction form is mainly fiber bending fracture, and fracture often exists below the machined surface. The validity of the simulation results is verified by the experimental micro on-line observation method.