Abstract: The undisturbed loess is significantly vulnerable to structural and dynamic damages. The earthquake-induced dynamic shear can destroy the original structure of the loess, causing soil particles to rearrange and compact, which macroscopically appears as seismic deformation. The dynamic torsional shear tests on Xi'an loess under different water contents and confining pressures are conducted to analyze the axial deformation. The factors such as dynamic shear stress amplitude, vibration frequency, water content and consolidation pressure are found to influence the seismic subsidence of the loess. An empirical formula is established to calculate the seismic subsidence deformation of loess, showing that the deformation increases with dynamic shear stress but at a decreasing rate. The water content and confining pressure are the crucial factors. The deformation increases with the water content and decreases with the higher confining pressure. The formula can be used to predict the seismic deformation of loess foundations.