When severe mandibular hypoplasia accompanying obstructive sleep apnea syndrome (OSAS) were treated by the orthognathic surgery, the results were quite successful not only in patients' profile, occlusion and functions, but also in the subjective and objective evaluations related to OSAS. The paper summarizes the methods and surgical procedures of treating OSAS with orthognathic surgery through the diagnoses and treatment of a group cases suffering from severe mandibular hypoplasia accompanying OSAS. Severe mandibular hypoplasia can cause not only the deformity and the disorder of occlusion, but also the OSAS. The advancements of mandible and hyoid with orthognathic surgery can improve the patients'prfile, occlusion and expand the patency of upper airway, so it can cure OSAS.