Obesity can affect the respiratory function of the patient. During nighttime sleep, apnea occurs, causing obesity hypoventilation syndrome during the day. Although not every obese patient develops apnea during nighttime sleep and not every patient with sleep apnea syndrome is obese, a strong relationship does exist between obesity and sleep apnea. Fat deposits in the neck can reduce the caliber of the upper airway, and the airway is more likely to collapse and become obstructed. Many foreign studies have found that the occurrence of sleep apnea is closely related to the circumference of the neck, and the more fatty deposits in the neck and the thicker the neck, the more likely sleep apnea occurs. Magnetic resonance examination found that the fat deposition around the airway increased in obese people, and the application of laryngoscopy to obese patients with sleep apnea syndrome found that the soft tissue wrinkle marsh in their throat increased and the inner diameter of the upper airway decreased significantly. Fat deposition in the thorax and abdomen of obese patients causes increased respiratory load, decreased thoracic compliance, diaphragm elevation, and decreased respiratory efficiency, so that many obese patients become short of breath and sweaty when they move. Sleep apnea and obesity aggravate each other, forming a vicious circle. It can be said with certainty that with weight loss, the patient’s sleep apnea can be significantly improved. However, in clinical work, it is not easy to make obese patients with sleep apnea syndrome lose weight, and some patients gain weight at a more significant rate than normal people. Long-term hypoxia and poor sleep lead to disorders in the brain that control the central function of food intake and body metabolism, coupled with the patient’s salivation, reduced activity and energy consumption, the increase in obesity is inevitable. In turn, obesity aggravates sleep apnea, and the cycle repeats itself, forming a vicious circle. Therefore, while emphasizing weight control, we should actively treat apnea through positive pressure ventilation to interrupt this vicious circle in order to receive twice the result with half the effort. Obesity will not only affect the respiratory function of people in the sleep state, another 5% to 10% of obese people will also have insufficient ventilation during the day, medically known as obesity hypoventilation syndrome. The main clinical manifestations of people with this disorder are: 1, obesity 2, daytime drowsiness. 3. Breath-holding and hypoventilation. 4. Increased red blood cells in the blood and increased hemoglobin. 5.The discharge of carbon dioxide from the blood is obstructed and the level is significantly increased. 6.Most of them have apnea during sleep. 7.Severe cases present with bilateral lower limb edema and right heart failure.