During the operation of cars, aerodynamic drag is a factor that affects the stability, balance and working efficiency of the vehicle. Therefore, aerodynamic characteristics are always concerned by manufacturers in the world today in the design process to reduce the drag of the vehicle and that is the main goal of this article. Research using Solidworks to build a 3D model of the vehicle from the 2D drawing of the original sedan car, applying the finite element method (FEM) by Flow Simulation module to investigate the pressure and velocity distribution around the model. Then the shape of the side mirrors and tilt angle of vehicle A-Pillar were changed to reduce the vehicle's aerodynamic drag from comparing the aerodynamic characteristics of the two models. Simulation analysis shows that compared to the original model, the improved model has a reduced drag force of 4% and a drag coefficient of 7.1%. The results serve the research and design of vehicle models to ensure high efficiency of vehicle performance.