A discrete element method(DEM) model of polyurethane ballast bed based on bonding force chain unit was proposed in this paper, based on which, a comparative analysis between common ballast bed and polyurethane ballast bed under cyclic loading was conducted. The results show that polyurethane can lessen the ballasts bed cumulative settlement by reducing the residual deformation and improving the contact status of ballasts. Besides, polyurethane can also increase the dynamic displacement of the sleeper.