Abstract: For different distributions of the fiber bundles in matrix materials，a micromechanical model was developed to investigate the effective properties of the composites. The composites consist of a solid matrix and fiber bundles. It is assumed that the composite has a periodic microstructure and the contact between fibers in the fiber bundle is smooth. The stiffness coefficients，transverse Young‘s modulus，shear modulus and Poisson ratio of the composites are calculated by the two-scale expansion method. The numerical results are compared with the experimental data. It is indicated that the distributions of the fiber bundle can directly affect the effective properties of the composites.