This paper studies the influence of the accelerated overtaking process on the vehicles’ transient aerodynamic characteristics,through 3-D numerical simulations with dynamic meshes and sliding interface technique.Numerical accuracy is verified by experimental results.The aerodynamic characteristics of vehicles in the uniform overtaking process and the accelerated overtaking process are compared.It is shown that the speed variation of the overtaking van would influence the aerodynamic characteristics of the two vans,with greater influence on the overtaken van than on the overtaking van.The simulations of three different accelerated overtaking processes show that the greater the acceleration of the overtaking van,the larger the aerodynamic coefficients of the overtaken van.When the acceleration of the overtaking van increases by 1 m/s2,the maximum drag force,side force and yawing moment coefficients of the overtaken van all increase by more than 6％,to seriously affect the power performance and the stability of the vehicles.The analysis of the pressure fields under different accelerated conditions reveals the cause of variations of the aerodynamic characteristics of vehicles.