Abstract: Using numerical simulation technique, the authors study the effect of the specimen size on stress distribution and fracture properties of the interface between the fiber and matrix for the fiber pull-out test. The effects of the embedded length of the fiber in the matrix and the wrapped thickness of the matrix around the fiber were considered. On the assumption of perfect interface of fiber and matrix, the numerical analysis for the interfacial shear stress and normal stress of the test specimen with different dimensions is performed. For the whole process of interfacial crack growth, the energy release rate was calculated. All materials are assumed to be linearly elastic solid. It is shown that the size of the test specimen affects dramatically the distribution of stresses and the fracture properties of the interface.