Abstract: To determine the relationship between the macroscopic behavior of mufti-phase materials and their microscopic structure is nowadays an important subject of computational mechanics.In this paper,the efficient quadratic isoparametric boundary element and the mufti-region technique were adopted to solve the macroscopic elastic modulus of a biphase medium with random order,The numerical results were compared with several common analytical formuli so as to provide a basis for appreciating the reliability of those, expressions.It can be seen that the BIM method possesses a great potenial in computational mechanics of conlposite materials.