In general, CFD analysis with porous media is precise enough to simulate airflow behavior in a heat exchanger core, placed in the engine room of a 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 the analysis of airflow in vehicle engine room. The concept of a new modeling 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 in the same conditions of the actual product. With this concept, airflow with an oblique angle hits the inner walls of tubes and passes through a core with changing the direction. Next, the concept of the new modeling is to reproduce the air pressure loss in actually-shaped fins and shorten computation time, and therefore, we use a porous medium for the modeling of the fins instead of the product form modeling (for air pressure loss computation) to combine with the modeling of 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 for air pressure loss computation, so that the turbulent airflow in 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 in the same conditions. When compared with the experimental results of the airflow velocity, the initial computation precision rate of 84% was improved to 98% with the new model.