Simplified mechanical model of tubular pile or closed diaphragm wall is proposed base on elasticity mechanics. The stress components of piles in two load conditions are solved by semi-inverse method at first. One load condition is that uniform vertical shear stress acted on the left and right sides of pile shaft

another is uniform vertical shear stress acted on the pile top. According to superposition principle

the stress components of the pile with unit shaft resistance on both side and vertical load on the head are solved. The calculating formulation of axial force and unit shaft resistance are deduced; and good identity has been achieved between the formulation and traditional method. When uniform vertical shear stress is not equal on both sides

the stress components of the vertical loaded pile are also solved according to superposition principle. Then an analytical solution of unit shaft resistance-axial strain relationship by using semi-inverse method is obtained. Application of the analytical solution is illustrated with a model test of closed diaphragm wall. This solution will provide theoretical basis for data processing of outer and inner axial strains which are measured in the model test of axial loaded cast-in-situ tubular piles or closed diaphragm wall. Thus true and accurate test result can be provided for the research on foundation-soil interaction.