A comprehensive three-dimensional numerical model was developed to study the gas/solid flow behaviors in a pulmonary airway affected by chronic obstructive pulmonary disease (COPD), a high morbidity lung disease and the patients of which suffer from respiratory difficulty caused by narrowed airway. The gas phase was modeled with laminar computational fluid dynamics (CFD) model and the particle phase was modeled with discrete phase model (DPM). Computational gas-solid flow behaviors in a three-generation airway were validated with experiment. After that gas/solid flow characteristics in an obstructed four-generation model were investigated by simulations. The air flow patterns and flow rates changing along the time series of transient inhalation and particle deposition patterns and efficiencies of the obstructed tube and adjacent generations under real inhalation condition were compared with the steady inlet results. It is found that air flow rates of the obstruction and its downstream generations reduce due to the stagnation and recirculation zones development with unsteady inhalation. Deposition area could enlarge and become more scattered than steady inlet. Secondary flow may contribute to the particle deposition in the inflamed airway for real inhalation. The deposition efficiency outcomes of the constricted tube indicate that transient inhalation condition may be more appropriate for COPD or similar obstructed airway simulation than steady inlet condition. (C) 2011 Elsevier B.V. All rights reserved.