There is a need to reduce vehicle's running resistance through aerodynamic performance in terms of having less negative impact on the global environment. In the Accord full model change, the package design is changed, so it is an opportunity to propose methods for improving aerodynamic performance. During the preliminary study, phenomenon analyses were conducted to identify areas that have a significant effect on aerodynamics by using a 25% scale model of the previous model. Based on more than 500 variation measurements as parameter study, the analysis was conducted using computational fluid dynamics (CFD). A proposal was made to the package design. For development that began with the fundamental frame proposed in preliminary studies, wind tunnel testing using 25% scale model was conducted jointly with the Styling Design Office to achieve enhancement styling while also increasing aerodynamic performance. The reduction in drag by means of under-floor devices naturally involves smoothing the under-floor flow. It is also achieved by reducing longitudinal vortex drag. In the preliminary study, CFD calculations were conducted with under-covers of the maximum area to analyze the flow field. It was found that reducing the pressure in the area between the rear tires could reduce the total pressure loss region and reduce the longitudinal vortex drag behind the vehicle. The flow fields obtained in the preliminary investigation was achieved by using a resin cover location at the minimum height above ground between the rear tires. The results of flow field analysis led to improvement CDA of new Accord Hybrid by 8.3% compared to the previous model.