Abstract: The undisturbed loess has significant structural and dynamic vulnerability. Under the earthquake, the dynamic shearing action destroys the original structure of loess. The pore volume of loess is reduced and the soil particles are rearranged and compacted, and the macroscopic representation is the occurrence of loess response, which is called seismic deformation of loess. In this study, the dynamic torsional shear tests on Xi'an undisturbed loess are conducted under different water contents and confining pressures. The axial cumulative deformation of undisturbed loess under different experimental conditions is analyzed. The influence of dynamic shear stress amplitude, vibration frequency, water content and consolidation confining pressure on the seismic subsidence deformation of loess is discussed. In addition, the empirical formula for calculating the seismic subsidence deformation of loess is established on the basis of influencing factors. The results show that the seismic subsidence deformation of loess increases gradually with the action of dynamic shear stress, and the growth rate tends to decline. The water content and consolidation confining pressure are the important factors on the seismic subsidence deformation characteristics of undisturbed loess. Under the same dynamic shear stress, the seismic subsidence deformation increases with the increase of water content and decreases with the increase of consolidated confining pressure. And the empirical formula for the seismic subsidence deformation of loess can be used to calculate the seismic deformation of loess foundation.