Abstract: The transverse elasto plastic mechanical properties of fiber bundle reinforced composites were studied by using the micro mechanical model and finite element method. ITis assumed that the elastic fiber bundle is evenly distributed in the elastoplastic powerlaw hardening matrix and the contact between fibers in the fiber bundle is smooth. The effect of fiber bundling on the overall elasto plastic properties of composite material was investigated by comparing the results of fiber bundle composites with that of the single fiber composites. The numerical results for the Boron/Aluminum composite show that the transvers plastic deformation and tangent stiffness are considerably influenced by the fiber bundling. While the elastic properties of composites are microstructure insensitive.