Inclusion Criteria:  Clinical diagnosis of mild to severe OSA in the past year Agree to receive Transoral Robotic Surgery (TORS) Age between 20-65 years old.  Exclusion Criteria:  Body Mass Index ≧ 32 Drug abuse within one year Pregnant Severe obstructive or restrictive lung disease A history of malignancy or infection of the head and neck region and laryngeal trauma Craniofacial malformation Stroke Neuromuscular disease Heart failure Coronary artery disease Ongoing or uncontrolled chronic diseases Combine central or mixed types sleep apnea syndrome Other non-breath related sleep disorder.