In general, CFD analysis with porous media is precise enough to simulate airflow behavior in a heat exchanger core, placed in the vehicle. In a case when the airflow behavior is complex, however, the precision lowers according to our study. Therefore, we developed a new modeling method to keep high-precision and applied it to analysis of airflow in the vehicle. The concept is at first that the shape of tubes and the distance between the tubes are as the actual product so that the airflow with an oblique angle is to pass through a core. With this concept, airflow with an oblique angle hits the surface of tubes and passes through a core with changing the direction. Next, the concept is to reproduce the air pressure loss in actually-shaped fins, and therefore, we use a porous medium for the modeling of the fins instead of the product shape modeling to combine with the the tubes. Additionally, for more accurate computation of the air pressure loss, we place another porous medium for rectification computation in front of the first porous medium, so that the turbulent airflow between tubes are rectified to enter perpendicularly in the first porous medium. We changed the model of the heat exchanger core of typical cars to the newly developed model and re-conducted the CFD analysis. When compared with the experimental results of the airflow velocity, the initial precision rate of 84% is improved to 98%.