Objective：To observe the changes of structure and function of pharyngeal muscle in SD rats with altitude hypoxia induced obstructive sleep apnea syndrome （OSAS） , in an attempt to investigate the remodeling of pharyngeal space and the possible biomechanical mechanism of OSAS. Methods： Twenty-four SD rats（ 12 male and 12 female） were randomly assigned to 4 groups with 6 rats in each group. Rats in group A and B were male and those in group C and D were female. Rats in group A and C were placed in altitude chamber and treated with altitude hypoxia 6 h per day for 22 days. The pressure in the chamber was 53.9 kPa with an oxygen concentration of 10.0%-11.2%. Rats in group B and D, serving as controls, received no treatment. All rats were sacrificed on the 23^rd day. The open-angle and the inside diameter of rats＇ pharyngeal-ring and the pathology of pharyngeal tissues were examined in all rats. Results： The open-angles of rats＇ pharyngeal-ring of group A, B, C and D were （55±24）°, （ 15±8）°, （38±20）°, and （35 ± 15）°, respectively; and the inside diameters of the pharyngeal-ring（cm） were 0.4±0.2, 0.2±0.1, 0.3±0.1, and 0.3±0. 1, respectively. The open-angle and the inside diameter of rats＇ pharyngeal-ring in group A were significantly higher （P〈0.05） than those of group B, C, and D, with no significant difference found between group C and D. Microscopic findings showed that, compared with group B, the muscle fibers of group A were fatter and were arranged disorderly, with unclear transverse striation, dropsical and congestive subcutaneous tissues infiltrated with inflammatory cells. Local unclear transverse striation of muscle fiber was seen in group C; the muscle fibers in group B and D were orderly arranged and no inflammatory cells were seen subcutaneously, Electron microscope showed disarranged muscle fibers with dissolved myofilament, disturbance and disappearance of the Z line in part of muscle fibers, expanded sarcoplasmic reticulum, and slightly condensed muscle cell nuclei. Local myofilament dissolving was found in group C. Conclusion： Twenty-two days＇ intermittent altitude hypoxia can induce OSAS in SD rats through changing the structure and function of pharyngeal muscle and remodeling the pharyngeal space