In order to study the aerodynamic responses of a vehicle pitching around its front wheel axle, large eddy simulation (LES) is used to investigate the flow-field around road vehicle. The numerical method is validated by 1/3-scale wind tunnel model on steady state. The LES results keep good agreement with the wind tunnel data. Furthermore, LES is applied to simulate the sinusoidal-pitching motion of vehicle body with frequency 10Hz. It can be found that the aerodynamic force coefficient and flow field changed periodically when the vehicle body takes periodically motion, whose results are completely different from the quasi-steady simulation results. When vehicle body suddenly changes direction, the hysteresis effects of the flow is clearly shown through investigating the transient flow field, aerodynamics force coefficient and pressure coefficient. The hysteresis effects of the transient flow field is also studied by vortices visualization technical, and the transient flow field from space and time is further understood.