Aspiration is a commonly used medical technique in clinical practice, and there is no absolute limit to the length of aspiration cannula, and the appropriate length should be used for aspiration treatment according to the patient’s specific situation, which is generally 10-25 cm. most patients who need aspiration have impaired sputum excretion due to various reasons. Sputum from the respiratory tract cannot be adequately expelled and is prone to infection, and may also block the airway. If the airway is blocked, it can lead to asphyxia in serious cases and can endanger the patient’s life instantly. Therefore, sputum aspiration is necessary, and different aspiration methods such as transoral, nasal aspiration and artificial airway require different lengths of intubation. 1. transoral aspiration: the oral cavity is closer to the trachea, generally about 14-16cm, but if affected by the patient’s resistance, closed teeth and throat reflex, it will not reach the depth; 2. transnasal aspiration: the distance of transnasal aspiration from the trachea is longer, generally up to 23-25cm. If the patient does not cooperate with resistance or the mucous membrane of the nasal cavity is congested and edematous, the suction tube may only be inserted into the nasopharynx or pharynx, and may not necessarily enter the trachea; 3. Artificial airway: the catheter can be directly inserted into the trachea after tracheotomy, and usually 10-15 cm can reach the lower end of the trachea, even the left and right bronchi. In addition, it is difficult for the suction tube to enter the relatively deep lower airway, and clinical aspiration with the help of microscopic bronchoscope is often required. Choosing the outer diameter of the suction tube, which should not exceed 1/2-2/3 of the inner diameter of the trachea or tracheal tube, can ensure effective suction without harming the airway mucosa. During the process of sputum aspiration, attention should be paid to the observation of consciousness, consciousness, oxygen saturation, sputum sound and lung rales, etc. If there is any unexpected situation, the operation should be stopped and oxygen should be administered in time.