Abstract: Cyclic triaxial tests and post-triaxial shear tests of the Ningbo clay are carried out to examine the effects of different vibration states, confining pressures and dynamic stress ratios on the dynamic characteristics and the post-vibration strength weakening characteristics of soil. The results show that the development of dynamic elastic modulus and cumulative plastic strain under one-way loading (no tensile stress) is more significant than that under two-way loading (resulting in tensile stress). But the development of elastic strain is opposite. In the shear stage, there is a peak at the pore pressure-axial strain curve and shear dilatation of the specimen, which shows the characteristics of the over-consolidated soil. Decrease in the shear strength under two-way loading is more obviously than that under one-way loading because of the tensile stress. The post-vibration strength weakening parameters under two vibration mode of the Ningbo ④2 clay are determined.