The invention provides a brain part MRI image segmentation method. The brain part MRI image segmentation method is characterized in that a gray level image of a brain part MRI image to be segmented can be acquired; the gray values of different pixel points of the brain part MRI image can be used as the clustering centers, which are used to form the clustering center sets as the particles, and the optimization of the clustering center sets can be carried out by adopting the particle swarm optimization algorithm; every pixel point of the brain part MRI image belongs to the category having the maximum membership, and then the gray values of the pixel points of the same category are equal to the same gray value, and the brain part MRI image segmentation can be completed. The brain part MRI image segmentation method is advantageous in that according to the chaotic characteristic and the logic self-mapping function, the uniformly-distributed particle swarms can be initialized by adopting the logic self-mapping function, and then the quality of the initial solution, the stability of the PSO algorithm, the speed and the precision of the image segmentation can be improved; the chaotic searching can be carried out, when the particles are in the premature convergence state, and the premature convergence phenomenon caused by the stagnated state of the particles during the iteration process can be prevented, and the optimal solution in the range of the whole situation can be realized, and then the speed and the precision of the image segmentation can be improved.