We simulated the pulmonary airflow using a 1D model of branching airway based on the clinical CT images of lung. The pressure and velocity profiles were obtained by solving the equations of continuity and motion of air flowing in the elastic airway with the mechanics of lung parenchyma. There was no significant difference in the distribution of pressure in the airway between the results obtained 1D and 3D airway models. The individual-dependent airway resistance also found during the respiratory cycles. These results indicate that the 1D model can be applied to develop a model of airflow in the whole airway systems. We also examined to simulate the forced oscillation technique which measured the respiratory impedance to assess in patients with COPD.