Due to the energy crisis, one of the important challenges in the Auto industry is to reduce the fuel consumption of the vehicle. And the higher speed is, the more fuel consumption is taken by the aerodynamic drag. Mostly, the aerodynamic drag lies on the shape of the vehicle. Consequently, the improvement of the aerodynamics of vehicle shape, more precisely the reduction of their aerodynamic drag, becomes one of the main topics of the automotive researchers. For a container-truck, the three dimensions of the container are standard and unchanged, and the shape of cab is almost fixed by the aesthetic sculpt. For those container-trucks, aerodynamic additional equipments can decrease the aerodynamic drag evidently, especially the wind deflector. Accordingly, this paper describes a method which combines CAD, CFD, Approximate model and optimization carried out on the aerodynamic shape of a container-truck's wind deflector.