Objective To study the flow characteristics of the upper airway and force dynamics of the soft palate and uvula in a representative male OSAHS (obstructive sleep apnea hypopnea syndrome) patient during normal respiration. Methods A CT image-based reliable geometry model of the upper airway was established. Numerical simulation boundary conditions were determined by clinical data of sleep monitoring, and the low-Reynolds number turbulence model was adopted to calculate the flow movement during a complete respiration period. Results The flow characteristics of the upper airway were obviously different in the breathing process of OSAHS patient. During inspiration, the maximum velocity of airflow in the upper airway reached 9.808 m/s, and the maximum negative pressure of airflow reached -78.856 Pa. Backflow districts were found at top of the nasal cavity. The maximum pressure on the soft palate was -10.884 Pa, and that on the uvula was -51.946 Pa. The maximum shear stress on the soft palate and uvula was 78 and 311 mPa, respectively. During expiration, the maximum velocity of airflow in the upper airway was 10.330 m/s, and the maximum negative pressure was -51.921 Pa. Backflow was observed to appear both at the oropharynx and top of the nasal cavity. Specifically, clockwise backflow was remarkable at the oropharynx. The maximum pressure on the soft palate was 2.603 Pa, and that on the uvula was -18.222 Pa. The maximum shear stress on the soft palate and uvula was 51 and 508 mPa, respectively. Conclusions Oropharynx is most likely to collapse in the upper airway. Numerical simulation on the respiratory cycle can capture the salient backflow features of the flow field in the upper airway. The backflow in the upper airway directly affects the forces on the soft palate and uvula and the breathing fluency of OSAHS patients.