Abstract: In the paper the elastoplaotie coistitutive relations of unidirectional fiber reinforeed composite materials were modeled numerically.The finite dlement metheod based on elastie-viscoplastic coastitutive theories was presonted,thea the micromechanics model was used to study the nonlinear stress-strain relations of compodites of which the elastie-viscoplaastic matrix is reinforced by the elastic fibers.