Abstract: Based on the plastic flow theory of soils, an elasto-plastic constitutive model for describing the dynamic behavior of the saturated sands is developed. The total deformation of soils consists of three parts: elastic strain, plastic strain related to volumetric yielding mechanism and plastic strain related to shear yielding mechanism. The soil behavior in initial loading, unloading and reloading stages can be reflected by adopting different model parameters. The constitutive model can describe the behavior of saturated sands subjected to both monotonic and cyclic loading with reasonable accuracy.