In order to discuss the torsional behavior of single pile in layered subsoil, various bearing states (elastic and plastic) of the subsoil were considered, and the double broken line model (i.e., the ideal elastoplastic model) was used to simulate the load transferring law along the pile shaft.The plastic zone developmental depth in the subsoil was chosen as an independent variable to derive the solutions for the torque-twist angle curve at the pile top and the torque-angle distribution curves along the pile shaft in layered subsoil.A recursive algorithm was presented to calculate the torque and the twist angle with the computer program worked out as well.Based on the solutions obtained, the torsional behavior of the pile shaft in the single-layer and the double-layer subsoil was analyzed respectively.Finally, an engineering project was used to verify the present method and to carry out the parameter analysis.The result shows that the consideration of various elastic or plastic states of the subsoil will result in a more reasonable outcome, compared with engineering practice.Furthermore, for a constant torque T, the torsion angles φ at the pile top will decrease with the decrease of the shear modulus Gp and radius r0 of pile shaft.An obvious effect of r0 on the Tφ curve was observed, in which the torsional bearing capacity may be increased 4~6 times if the value of r0 was doubled and other conditions remained unchanged.The upper soil layer may be treated to improve the torsional performance with an advised effective treatment depth of 0.2 times the pile shaft length.