Abstract: For the graphite fiber reinforced aluminum matrix composite material prepared by vacuum pressure infiltration method, the representative volume unit cell was established by observing the microstructure characteristics. On this basis, a unit cell finite element model considering the ductile damage of the matrix and the interface damage and failure behavior is established. The research results show that the unit cell finite element model considers the failure behavior of the interface in the transverse shear deformation of the composite material, so the transverse shear elastic modulus obtained by the numerical simulation is slightly lower than the calculated value of the micromechanical formula. The interface damage occurs first and accumulates gradually during the transverse shearing process. As the shear strain increases, local damage to the interface occurs and induces damage to the matrix alloy near the fiber. In the final stage of shear deformation, the failure area of the matrix alloy between the fibers is connected to cause the overall failure of the composite material. Under the action of transverse shear load, interface debonding and matrix alloy failure near the fibers are the main mechanisms that cause the failure of composite materials.