PURPOSE: To investigate the factors influencing the severity of obstructive sleep apnea (OSA) in children and to elucidate the synergistic effects of upper airway comorbidities (chronic rhinosinusitis, nasal septum deviation and malocclusion) with tonsillar and adenoid hypertrophy on ventilation efficiency. PATIENTS AND METHODS: A total of 404 pediatric patients with OSA aged 6-10 years diagnosed between January 2022 and January 2025 were included in this retrospective cohort study and underwent logistic regression analysis to identify the risk factors for pediatric OSA. Three-dimensional upper airway models under various comorbidity states were constructed via cone‒beam computed tomography (CBCT), and postoperative airway resistance changes were calculated via computational fluid dynamics (CFD) simulation and simulated surgery. RESULTS: Grade 3 tonsillar or adenoid hypertrophy, the presence of comorbidities, and overweight/obesity were identified as independent risk factors for increased OSA severity. A dose‒response relationship was observed between the number of comorbidities and OSA severity, with the highest odds ratio (OR=9.392, 95% CI=2.459-35.875) for triple-positive comorbidities. CFD simulations demonstrated that tonsillectomy and adenoidectomy (T&A) significantly improved ventilation function across different OSA severities. Comorbidities influence airway resistance, with postoperative resistance in children with triple-positive comorbidities approaching preoperative levels in those without comorbidities. CONCLUSION: T&As hold therapeutic value for pediatric OSA patients, but comorbidities significantly mitigate surgical efficacy through synergistic effects.