Abstract: Through simulating the aerodynamics characteristics of a cabriolet and coupe by using validate CFD method, the reason was found that the extensive separation zone in the cabin results in the back-flow air around the cabin, which not only decreased the driving comfort, but also increased the drag coefficient of cabriolet. By lengthening the upper brim of windshield at an appropriate distance, raising the height of seat back, keeping the angel of the windshield around 33° can effectively cut off the reversed flow, improve the driving comfort, reduce flow separation zone, low down the drag coefficient (16%) and ameliorate the flow field of the cabriolet.