A spoiler is one of most important factors for secure Aerodynamic performance and recently is not any more option part for MPV/SUV/Hatchback, by reducing strength of rear wake zone and optimizing flow separation of a roof end to prevent increasing drag. Until now, Blow method in mold has been seen as a typical one for spoiler. But, most of automobile companies use the Injection type for reduction of cost and weight and for getting more complicated design. In this study, we can set a standard of engineering design in optimized position and distance between mounting hardware and in evaluating the stiffness for opened shaped spoiler as well as large sized exterior parts with high stiffness material and see the higher quality of it with panel and other parts than blow method typed one.