Due to children's lower oxygen reserves and higher oxygen consumption, sedation can easily lead to respiratory adverse events such as hypoxemia. It has been reported that the incidence of hypoxemia during pediatric bronchoscopy is high, highlighting that hypoxemia in pediatric painless bronchoscopy is an urgent problem requiring a solution. High-flow nasal cannula (HFNC) oxygen therapy delivers heated and humidified breathing gas with a precisely controllable oxygen concentration, at flow rates exceeding the patient's peak inspiratory flow, directly via unsealed nasal prongs. It is a simple, comfortable, effective, and non-invasive respiratory support method that has been widely adopted in clinical practice. However, the effectiveness of HFNC in pediatric sedation remains unclear. Therefore, this multicenter randomized controlled trial aims to evaluate whether HFNC can effectively reduce the occurrence of hypoxemia during sedated bronchoscopy in pediatric patients.