Automated segmentation of brain MRI image is an important computer based technology with wide applicability i n medicine field, and of great significance in the study of hu man brain diseases. There exists a variety of segmentation methods, such as the the thresholding method, the region growing method, and the clustering method, w hich are broadly applied to natural images. However, those methods are not as p owerful or practical as atlas-based method when applied to clinical medical ima g e. The development of the atlas-based method for brai n image segmentation is reviewed, and representative algorithms are introduc ed. The basic princi ples of these parcellation algorithms are described as well as the components of a state of the art segmentation system. On this basis, the segmentation pro cedures are introduced, and its various applications in clinical medicine are di scussed . Finally, the current status and the futu re potential of the automated segmentation′s applications in clinical medicine are summarized.