Abstract: In expansive soil stratum, soil swelling rate and stiffness varies obviously with depth. In deeper sites, the stress level of expansive soils is higher, which leads to greater stiffness and a smaller expansion rate. Based on the mechanism of pile-soil interaction, single pile analytical equations considering stiffness increase and expansion decrease along the depth of soil are derived by the load transfer method, and the solution is expressed in a Taylor series. Calculation results conform to the field and model test data, especially the mode of pile deformation, verifying the reliability of the solution. Under conditions of constant average expansion rate and average stiffness, the effects of displacement distribution mode and stiffness distribution mode to pile-soil load transfer are studied. Results show that the traditional assumption, of a constant swelling rate and stiffness distribution along the depth of soil, will significantly overestimate the pile axial force and displacement. The analytical solutions are used to discuss the critical pile head load also.