Abstract: The numerical model of the forward intake port of a commercial vehicle air filter was established, the internal flow field was simulated to obtain the information of the internal flow field of the forward intake port model and the model was validated with the experimental data. In addition, the grille angle, rain shield size and number of the forward intake port of were changed to examine its effect on the internal flow field. The results show that the simulation values of the forward intake port at different flow rates agree well with the experimental values, and the maximum error is within 15%. For the forward intake port with or without the rain shield, its pressure drop increases when the grille angle decreases. For a certain grille angle, the pressure drop of the forward intake port with the rain shield is about 200 Pa, which is higher than that of the forward intake port without the rain shield. When the structure of the rain shield is B in this study, the pressure drop of the forward intake port is 727 Pa, which is the smallest among all structures. When the structure of the rain shield is D, the pressure drop of the forward intake port is 761 Pa, which is the largest. The results also show that the effect of the number of the rain shield on the pressure drop is greater than that of the rain shield size.