Abstract: The unsteady flow field of a fastback car during starting process was simulated numerically with Computational Fluid Dynamics(CFD)method.The aerodynamic drags and drag coefficients under two starting accelerations were calculated using k-ε turbulent model and the first order upwind scheme.The results show that the aerodynamic drag increased significantly in the starting process and reached a maximum value in a very short period after starting.When the car ran steadily,the drag tended towards a constant value.The drag-coefficient decreased rapidly during starting and became steadily after completion of starting.In the process of staring,wake vortex formed gradually and the pressure difference between the front and back of the car became bigger.After running steadily,the difference became smaller.