Abstract: The size of modulus is directly related to the value of pre-consolidation pressure and the additional volume strain due to pile-soil interaction for geotechnical materials. First, the paper analyzes the main factors of constitutive models for the materials, considering its changes with depth and volumetric strain. Tensile modulus in Duncan-Chang constitutive model is revised based on the above analysis. Then, the mechanical model due to pile-soil interaction is established considering the effect of the displacement boundary of the interaction and the above-mentioned non-linearity of the materials. The theoretical solutions of soil displacement, strain and stress, are obtained based on the variation principle. Finally, comparisons are made to prove the reasonability of the results, using the classical CEM results and the passive soil pressure theory.