The equivalent continuous processing is done to multi-element composite foundation by composite material mechanics method, and the composite foundation is studied as transversely isotropic body, the constitutive relation of equivalent complex is established at first time. On the ABAQUS platform, the three direction seismic responses of multi-element composite foundation are studied by finite-infinite element coupling method. The results shown that: (1) the model of equivalent complex can reflect the working mechanics of the multi-element composite foundation; (2) with the increase of the total stiffness of the multi-element composite foundation, the max absolute values of horizontal accelerations and displacements decrease gradually. (3) With the increase of reinforced depth, the horizontal accelerations in reinforced area became small, but the displacements became big. The results can provide reference to the seismic design of structure.