The dynamic stress response of subgrade under moving train loads provides information on subgrade settlement prediction and condition evaluation. In this paper

a 3 D dynamic finite element（FE） model

which considered the interaction of wagon-track-subgrade

was firstly built. And then

the vertical irregularity track spectra of China’s three major lines were applied to simulate the track irregularity. Through numerical calculation

the influence of vertical track irregularity on dynamic stress at the subgrade surface was investigated. The distributions of peak dynamic stresses at three locations of subgrade surface（beneath the rails and at the track center） along the track under the passage of the trains with various axle loads were statistically acquired. The normal distributions of peak dynamic stresses on subgrade surface were verified. The maximums of peak dynamic stresses were forecasted.The results indicated that dynamic stresses on the subgrade surface were asymmetric along the center of subgrade surface

attributed by the random distribution of track irregularity. The peak dynamic stresses were found to follow the normal distribution along the track. The dispersion of peak dynamic stresses gradually increased

and the distribution curve of peak dynamic stresses became steeper with the increase of axle load. The computing peak dynamic stresses were consistent with field test data

indicating that the3 D dynamic FE model and statistical analysis method were reasonable. The research results provide the basis for the reliability analysis of the dynamic deformation and accumulated settlement of subgrade.