Abstract: The dynamic characteristics of the undisturbed loess in Haidong area of Qinghai Province are studied by using the British GDS bidirectional dynamic triaxial test system. The test results show that: when the dynamic strainε_d is smaller than 1%, the dynamic shear modulus decreases sharply with the increase of the dynamic strain, while it decreases slowly with the increase of the dynamic strain and tends to be stable at the later stage when the dynamic strainε_d is larger than 1%. The dynamic shear modulus increases with the increase of the consolidation confining pressure, consolidation stress ratio and loading frequency, in addition, the increasing amplitude decreases with the increase of the strain. When the dynamic strainε_d is smaller than 0.5%, the damping ratio increases rapidly with the increase of the dynamic strain. When the dynamic strainε_d is larger than 0.5%, the damping ratio increases slowly with the increase of the dynamic strain. When the dynamic strain is small, the consolidation confining pressure, consolidation stress ratio and loading frequency have no clear influence on the damping ratio. With the increase of the dynamic strain, the damping ratio decreases with the increase of the confining pressure and loading frequency, however, it increases with the increase of the consolidation stress ratio.