In recent years, number of deaths due to chronic obstructive pulmonary disease (COPD) has been increasing all over the world. COPD is an inflammatory disease of the lungs caused in part by long-term inhalation and exposure to harmful substances such as tobacco smoke, and its general pathological symptoms are airflow limitations. Inhaled medication is one of the well-known pharmacological treatments for COPD. In order to consider the pharmaceutical particles deposition in the lungs numerical simulations have been conducted to analyze the macroscopic flows in the airways. Most of these lung models were constructed based on the geometrical similarity of the airways, such as the Weibel’s model, which is divided 0th order to 23rd order for simplicity. Therefore, it is important to consider airflows in the lung using patient-specific models. In this study, we created airway models from medical image data and analyzed airflows using CFD solver AcuSolve. As a fundamental study, the airway models up to third generations were used for the airflow analysis. The governing equations are the continuity equation and the incompressible Navier-Stokes equation in fully three dimensions. The working fluid was assumed to be a single-phase gas, and the airway wall was set rigid. In addition, no gravity effects were taken into consideration. Then, the physical quantity of the flow field (i.e., velocity profiles, secondary flow, flow rate distribution etc.) was evaluated and compared among the models. In addition, pulmonary airway models were classified according to the severity of COPD and relationship between their geometric features and internal flow was investigated in detail.