Abstract: The unsaturated intact loess has remarkable structured properties. Its structure is damaged by wetting and cyclic shear action, which leads to the development of shear and subsidence deformation of loess under earthquake. Based on the dynamic torsional shear tests on hollow cylindrical specimens of intact loess under different consolidation pressures, the dynamic shear-strain relationship from small to large strain, the dynamic shear modulus and the dynamic damping ratio of loess are tested and analyzed. The relationships between dynamic shear stress and shear strain, dynamic shear modulus and dynamic damping ratio and the failure strength of loess under gradually increasing cyclic torsion shear action are measured. The variation rules of dynamic shear modulus of loess under different consolidation pressures and moisture contents are obtained in the shear strain range of 10^-5~10^-2. It is shown that the maximum dynamic shear modulus increases with the initial structural index of loess. An approximate linear relationship among the maximum dynamic shear modulus, the structural index and the consolidation pressure is established. The damping ratio of loess changing with the dynamic shear strain logarithm under different consolidation pressure and moisture contents is released. The shear failure characteristics of cylindrical loess samples under cyclic torsional shear action are constituted by two groups of shear failure planes.