Track irregularity is the most important excitation source of wheel-rail system. The vibration characteristics of vehicle components and track components are analyzed in this paper under the condition of track irregularity by establishing the vehicle - track vertical coupling model. And the establishment of vibration differential equation and numerical simulation method for solving vibration response are described in detail. Finally, the results are given by MATLAB. The method is of great significance for evaluating the dynamic track irregularity and vehicle’s vibration at different running speeds.