The airflow in human pulmonary airways is numerical simulated using a simplified model in order to get the flowcharacteristics. This four generation model from the 3rd generation to the 6th generation, which the wall isassumed to be rigid andsmooth,is in the same planar with rounded carinal ridges, computations are carried out with the mouth inlet flow rate from 15 to60 l/min, and the corresponding inlet Reynolds number is from 500 to 2000, which means the airflow is three-dimension andincompressible laminar flow, different inlet boundary condition are taken to research the influence to the airflow field. Theairflow patterns, flow distribution and pressure drop are selected to demonstrate the airflow characteristics.In this work, wefound out the main airflow skewed to the inner wall of bifurcation and new boundary condition was generated, strongsecondflow was observed in theairways, especially in the medial airways, the airflow ratein lateral airwaysare less than the medial ones,inlet velocity profile mainly affect the medial airways but slightly to the lateral ones, the totalpressure drop is closed related tothe mass flow rate and inlet velocity profile, the results show this model is detailed behavior supported for the whole lung, it is anecessary step for analyzing particles transport and deposition in human lung.