Determine the site(s) of upper airway obstruction and the influence of sleep stage on the pattern of obstruction with upper airway (UA) pressure measurement. Analyses the clinical value of UA pressure measurement and it's influenced factors.30 OSAS patients underwent UA pressure measurement during polysomnography. Multisensory pressure catheters with five solid-state ultraminiature sensors were insert through patients' upper airway to esophagus, The sensors were located at the nasopharynx, oropharynx, tongue base, hypopharynx and esophagus and the lower limit of UA obstruction was determined relying on the observed pressure pattern.(1) During inspiration, obstruction occurred associated with a increased negative inspiratory pressure inferior to the site of obstruction and a disappeared negative inspiratory pressure above the site of obstruction. (2) Three patterns of obstruction were observed. 1. The site of obstruction was located at the level of the palate. 2. The level of the palate and tonguebase obstruction all present. 3. Nasopharyngeal obstruction soft plate obstruction and tongue-pharynx obstruction all present. (3) The factors which affected these measurement are 1. The catheter were placed by observation with a fiberoptic endoscope to keep the sensors located at the correct position. 2. Catheter plugging with secretions need to be prevented.UA pressure measurement can objectively identify the level of obstruction during sleep.