The accuracy of lung segmented results is important in actual clinical application. However, all kinds of segmentation methods can not be uniform for all the chest CT (Computed Tomography) images because of the irregularities and diversity of lung disease, as well as significant differences in the anatomy of the human chest. Lung parenchyma segmentation studies still have a great challenge. Based on the analysis of domestic and international research, a new lung segmentation method is presented by combining with 3D region growing method and improved convex hull patching algorithm. Firstly, the 3D region growing method is adopted for the rough segmentation of lung CT images. Then the refining work is done to the segmented results. The connected domain labeling and morphological methods are used to remove the trachea and main bronchi to get the pulmonary parenchyma mask. The improved convex hull algorithm is presented to repair and smooth the concavities of lung contour. Finally, the segmented results can be gotten. The improved convex hull algorithm can repair the concavities of lung contour effectively in comparison with the convex hull algorithm and the rolling ball method, and the segmentation precision of results is very high after repairing.