Objective To investigate the dynamic changes in the upper airway that cause the obstructive sleep apnea-hypopnea syndrome by measuring the variations of upper airway pressures in the treatment of Erchen Decoction. Methods 53 patients with OSAHS examined polysomnography with upper airway pressure at the same time. divided into 2 groups， the treatment group was treated with Erchen Decoction， the control group was treated normally such as weight loss， each group treated for 3 months， reexamined polysomnography and upper airway pressure， contrasted the data of before-and-after. Results The negative pressure fluctuations of P1 and P2 decreased， there are significant difference between before-and-after. Conclusion With treatment of Erchen Decoction， the upper airway negative pressure of obstruction reduced， and then eased the data of LSaO2 and AHI， it’s invalid to the data of BMI for treatment group.