Abstract: Dynamic and mathematical models of multidefective piles in nonhomogeneous soil are established,in order to simulate general behavior of a single pile which is dynamically tested at low strain.By means of Laplace transform and matrix thoery,an exact transfer function of pilesoil system is derived.Further,the mechanical admittance expression,frequency and time domain expressions of the velocity of the pile head subjected to axial impact loading are gained.The validity of this approach is verified through dynamic tests on some engineering piles in the field,and the theoretical predictions match the response of the piles.Single factor analysis method is presented for interpreting complicated mechanical admittance curves.