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OSAHS (Obstructive Sleep Apnea Hypopnea Syndrome) is a respiratory disease mainly characterized by limited and repeated pauses of breathing in sleep. Currently, the optimal treatment is to apply CPAP (Continuous Positive Airway Pressure) ventilation on the upper airway of the patient through a household respiratory machine. However, if the ventilator mask is designed improperly, it might cause the residue and repeated inhalation of CO2, which will exert an adverse impact on the therapeutic effect. Present research numerically analyzed the CO2 transportation inside a commercial ventilator mask (Mirage SoftGel, ResMed, Australia) based on the reconstructed 3D numerical model of a volunteer's face and performed the improved design of the ventilator mask in terms of the CO2 residual concentration below the nostrils. The fluid dynamic analyses showed that at the end time of expiratory, the CO2 residual concentration below the nostrils is close to 4%. To improve the therapeutic effect, we changed the position of the exhaust holes and found that by moving the exhaust holes to the bottom of the ventilator mask, the CO2 residual concentration below the nostrils would be reduced to no more than 1%. This study established a near physiological computational model and provided a new method for the individualized design of the commercial ventilator mask. [ABSTRACT FROM AUTHOR]