Objective To investigate the imagery changes of the upper airway and the surrounding soft tissues of local adults with non- apnea who used snore guard and to provide experimental data for the clinical diagnosis and treatment of obstructive sleep apnea syndrome（OSAS）. Methods Thirty students with non- apnea from Hebei medical university were chosen, and magnetic resonance imaging（MRI） was used to measure the changes of the upper airway and the surrounding soft tissues after snore guards were used. SPSS 10.5 software was used to analyze statistically. Results After the snore guard was put into oral cavity, the change of the average section and volume of the nasopharynx, the palatopharynx, the hypopharynx and the glossopharynx were statistically significant. The average sagittal size, the average horizontal size of the nasopharynx, the palatopharynx, the hypopharynx and the glossopharynx were increased statistically. The ratio of sagittal size, the horizontal size in the hypopharynx and the glossopharynx changed statistically important. There was a decrease of the soft palate, the shape, the height, and the length of the tongue, the difference was statistically significant. The results demonstrated that snore guard affected the upper airway mainly by changing the volume and the shape of the upper airway, there was an obvious increase of the pharynx. The results also showed that snore guard could increase the width（both sagittal and horizontal） of the upper airway and could change the shape of the surrounding soft tissues, which caused air way more smooth. Snore guard could make the indexes of soft palate and tongue change decreasingly, resulted in the straight stand up of the tongue and the forwardness of the soft palate. Conclusion Snore guard is an effective and convenient instrument for treating the patients with OSAS.