In this paper, a finite element numerical model of thermal-hydro-mechanical of energy piles under multi-layer geological conditions was established, and field tests of ultra-long energy pile (1000-mm-diameter, 44-m-long) were carried out to reveal the temperature distribution and mechanical properties of energy pile under typical working conditions. Based on the analytical results, a softening shear model of the energy-soil interface under the condition of large shear displacement was proposed with the load transfer method, and the reliability of the model was verified. The model can simulate the shear-displacement relationship of the pile-soil interface under different geological conditions.