The one-box type automobile's stability on the highway is often influenced by encountering crosswinds or when passing large automobiles such as trucks and buses. This causes the automobile to behave unexpectedly. Many experiments for improving this situation have been carried out. In this respect, the analysis of transient aerodynamic characteristics is important for automobile safety and stability on the highway. Conventional transient aerodynamic simulations require a supercomputer and about million grid points. Also there were few case studies that dealt with situations such as plunging into crosswind and passing an automobile.In this paper, a transient aerodynamic simulation by using a sliding mesh of discontinuous interface and the Arbitrary Lagrangian-Eulerian (ALE) method is presented. This method uses the k-ε turbulence model and the third-order upwind scheme, which is introduced to the convective term of the Navier-Stokes equation to improve the flow field and pressure distribution. It takes 100 hours to get the total transient results by using an engineering work station (EWS). Calculated yaw characteristics in a crosswind are in good agreement with experimental results.Furthermore, we have simulated the effect of an active spoiler in a crosswind, and the aerodynamic characteristic of passing a one-box automobile are carried out.