Conclusion: From aspect of fluid dynamics, expanding patients' nasopharyngeal coronal-sectional area to 48.3-54.7% of normal area will bring the airflow velocity back to normal in adenoidal hypertrophy children. It might provide a suggestion for adenoidectomy range selection and whether total resection is necessary. Objectives: To evaluate the nasopharyngeal airflow characteristics in pediatric OSA patients with adenoidal hypertrophy, and to explore the proper resection range for adenoidectomy Method: Nine OSA patients and four normal children were recruited. The CT scans of their upper airway were collected and used to construct three dimensional models for fluid dynamics analysis. Using computational fluid dynamics, indices such as velocity, pressure, and coronal-sectional area were calculated. Results: Compared with the normal, the OSA children showed three characteristics in nasopharyngeal: the airflow velocity was significantly higher (p < 0.05), the coronal-sectional area was significantly smaller (p < 0.01), while pressure showed no difference (p > 0.05). In a study of the relationship between velocity and coronal-sectional area, this study investigates different coronal-sectional areas from 30-300mm(2). It was found that, when patients' nasopharyngeal coronal-sectional area was expanded over 155-170mm(2), namely 48.3-54.7% of normal area, airflow velocity in nasopharyngeal showed no difference than normal.