Abstract: The researches indicate that the Biot theory has model defects in describing the mechanical characteristics of saturated soil, and that it is more reasonable to describe the mechanical behaviors of saturated soil by using the theory of porous medium. Based on the theory of porous medium, the torsional vibration of the saturated soil is solved by the Novak plane strain hypothesis, and also obtained is the ring displacement of saturated soil. The torsional dynamic impedance is obtained by the stress-displacement relationship of the soil skeleton, the torsional vibration of single pile in saturated soil is investigated based on the torsional dynamic impedance, and the influence of parameters on the properties of the torsional complex stiffness is also discussed. The results show that the curves of torsional complex stiffness varying with frequency have peaks, the system of pile-soil has resonance, and the length-diameter ratio and modulus ratio have great effect on the torsional complex stiffness, while the influence of coupling coefficient is little, but it cannot be negelected.