With the development of high-speed railways，ballastless tracks are widely applied，and the dynamic characteristics of the subgrade form the basis for design，construction，and maintenance of the ballastless track/subgrade system.In a sense，the distribution rule of dynamic response under the action of train loads and the influence of subgrade parameters lags far behind the construction of high speed railways in engineering because it is highly complicated.The dynamic system, which includes rail，track，and roadbed，is so complex that it cannot be solved by available theory.In this paper，the numerical simulation method is introduced to describe the dynamic action of a roadbed bearing high speed rail loads.A three-dimensional（3D）finite element model of the track-subgrade system is established with the aid of ANSYS for dynamic response of ballastless track subgrades bearing vehicle dynamic loads and load input behavior.Moreover，by using the choice method and basis of unit type，a constitutive model of subgrade and material parameters is established.According to the distribution mode and behaviors of vehicle dynamic load and load input characteristics，a two-car，eight-wheelset vehicle model was introduced to obtain contact pressure time-history curves of fastening when two bogies pass between neighboring cars through Fourier transform.In addition，the rationality and applicability of the model are verified according to the data obtained from in situ testing.Vertical dynamic stress，dynamic displacement，and dynamic acceleration are calculated for a CRTS II type slab ballastless track and a double-block ballastless track when a passing train has a speed of 300 km/h and an axle load of 170 kN.Furthermore，the relationship between the response laws and the rail-subgrade construction are analyzed.Interrelated analyses reveal that vertical dynamic stress，dynamic displacement，and dynamic acceleration decay with an increase in roadbed depth.Dynamic acceleration decay deceleration was the fastest.In addition，the type of track influenced the dynamic response only at the top of the roadbed.