Abstract: The finite element method is an important analysis in the researches on the interaction between super-structure and base,but the analysis is often difficult to deal with because the dispersed region required is large,the number of element needed is too large when the pile-soil system is compartmentalized into many elements,and the limitation of computer software or hardware is caused.In this paper the grouped piles foundation was treated as a kind of composite materials in terms of the equivalent continuum established method,and then the constitutive relation of the composite materials and the equivalent composite model were established.Compared with the computated results obtained by “the separated model” and “the composite model” on the basis of the analysis of finite element method,it was shown that the equivalent composite model reflected the load transfer mechanism of grouped piles foundation well,and the equivalent continuum method was proved to be feasible huge to grouped piles foundation.The equivalent composite model adopted could reduce the number of infrastructure base elements and accordingly develop the maneuverability of interaction between super-structure and base in use of the finite element method.