Abstract: The diaphragm is the most important respiratory muscle. Diaphragmatic dysfunction is associated with the occurrence of pulmonary complications and poor prognosis of patients, which can increase the patients' hospital stay and even mortality. Diaphragmatic ultrasound can evaluate the structure and function of the diaphragm by observing the movement mechanics of the diaphragm, measuring diaphragm thickness, diaphragm thickening fraction and diaphragm excursion, and eventually assist clinicians in decision-making. It has potential value in identifying diaphragmatic dysfunction, predicting the time of withdrawal and extubation of patients with mechanical ventilation, predicting postoperative pulmonary complications, evaluating patient-ventilator synchrony and rehabilitation effect.