Abstract: The average elastic-plastic behavior of composite materals is discussed.The general formulation of the composite material with prolate spheroid inclusion and with the matrix is shown when the matrix and the inclusion are isotropic materials.The volume of any inclusion is smaller than that of the matrix,and the inclusions fit tightly against the matrix.The overall average Young's modulus,average shear elasticity and average Poisson's ratio of the composite material with prolate spheroid inclusions are shown,and it is proved that this composite material is nonisotropic.The way to increase the average elastic moduli of the composite material is also found.