The narrowest part of the respiratory tract is the glottic fissure, which is located in the pharyngeal region of the upper airway. The glottic fissure is the gap between the vocal folds on both sides of the pharyngeal cavity and the base of the arytenoid cartilage bone and the vocal fold prominence. It becomes diamond-shaped during significant breathing movements. The length of this area is about 23 cm for a normal adult male and 17 cm for a female, and because it is a very narrow part of the airway, it can be easily obstructed by pathological factors or foreign body inhalation, and even suffocation can easily occur. In this case, the necessary tracheal intubation is needed urgently to give mechanical ventilation, so when intubating the trachea, attention should also be paid to the relatively difficult passage through this narrow area.