Patients meeting the criteria of obstructive sleep apnea were included, and all patients signed informed consent, which met the requirements of the ethics Committee of our unit. All subjects were hospitalized patients. Subjects were randomly enrolled into High-flow Nasal Cannula Oxygen Therapy group or Continues Positive Airway Pressure group for 3 days of treatment. Sleep monitoring was performed on the first and fourth day of enrollment.

Inclusion Criteria:

1. There were typical symptoms of sleep snoring at night with apnea and daytime sleepiness (ESS score ≥9). Stenosis and obstruction in any part of the upper airway were observed on physical examination, with AHI≥5 times /h.
2. For patients with no significant daytime sleepiness (ESS score < 9), AHI≥10 times /h.
3. Patients with AHI≥5 times /h had one or more OSAHS complications, such as cognitive impairment, hypertension, coronary heart disease, cerebrovascular disease, diabetes and insomnia.

Exclusion Criteria:

1. Patients who cannot tolerate non-invasive ventilator or transnasal high-flow oxygen therapy.
2. Ongoing treatment may affect sleep, such as sedatives, hypnotics, muscle relaxants, etc.
3. Hemodynamic instability.
4. Severe respiratory diseases.