Abstract: A coupling dynamic model for train-ballastless track on subgrade was derived based on the vehicle-track coupling dynamics to analyze the dynamic performances of the ballastless tracks and the stiffness of transition tracks.In the model,the tracks are regard as Bernoulli-Euler beams on discrete elastic supports,and the slabs and the RC(reinforced concrete) roadbed as elastic plates on an elastic foundation.The movement equations of ballastless tracks on the subgrade were also derived.The dynamic performances of slab track and the stiffness of the transition tracks on Suiyu(Suining-Chongqing) railway were investigated with the model and movement equations.The results show that the vertical and horizontal wheel-rail forces,derailment coefficient,rate of wheel load reduction,dynamic stresses in CA mortar and subgrade surfaces are less than the permissible values when a high speed passenger train,a heavy freight train or an ordinary freight train passes.On the transition section between the ballastless track(slab track or bi-block track) and ballasted track,the change rate of rail deflection is less than the permissible value,0.300 mm/m when a high speed passenger train passes,indicating that the stiffness design of the transition tracks is rational although the change rate of rail deflection is slightly greater than the permissible value when a heavy freight train passes.