Abstract: In order to describe the dynamic characteristics of saturated soft clay under cyclic loading, an egg-shaped one-sided bounding surface model is established. First, by introducing the egg-shaped bounding surface, the model overcomes the defect that the direction of the plastic strain increment at the corner of the Cambridge-type bounding surface is not clear, and degrades the egg-shaped bounding surface into different types including the Cambridge form and the elliptical form, which reflects the universality of the model. Next, the model adopts the associated flow rule applicable to saturated soft clay, uses plastic volumetric strain as the internal variable in the isotropic hardening process, and uses the general isotropic hardening rule and the mapping rule of the moving mapping center to accurately describe the soil stress induced anisotropy and plasticity during unloading. Then, the method for determining the model parameters is clarified, and the influence of each model parameter on the dynamic characteristics of saturated soft clay is explained through parameter analysis. Finally, using the one-way cyclic triaxial tests on kaolin clay under undrained condition and the isotropic consolidated tests on Itsukaichi marine clay under undrained condition, the simulated values are compared with the measured ones. The results show that the simulated results agree well with the test ones, and the proposed model can reasonably describe the characteristics of saturated soft clay under undrained cyclic loading and static shearing loading.