Abstract: During wind noise development for a vehicle, an airflow separation and reattachment phenomenon was observed on the A-pillar surface. Premature airflow separation occurred on the A-pillar surface, significantly deteriorating cabin wind noise under crosswind conditions. It is proposed that reducing the A-pillar’s binocular obstruction angle—thereby decreasing its width—may lead to a sharp deterioration in A-pillar-related wind noise. Therefore, a comprehensive identification and decomposition of the A-pillar’s characteristic parameters were conducted. By analyzing the influence of these parameters, the A-pillar surface geometry was optimized. Wind tunnel tests verified an 8.8% AI reduction in cabin wind noise under crosswind conditions and a 2.3% AI reduction under headwind conditions, while also eliminating the risk of localized noise around the A-pillar. Finally, key design considerations and recommended parameter ranges are briefly summarized.