In view of the problems that the target border always appears too fuzzy to be detected, a novel method of brain tumor segmentation is proposed based on spatialfrequency domain image enhancement. The method is composed of the spatial and frequency domain enhancing process and the detecting process. In the enhancing process, the directional filter band, neighborhood and histogram equalization are combined to overcome the defect of contrast reduction caused by directional filter and the defect of details vagueness caused by histogram equalization. Then in the detecting process, a method of image segmentation is applied to find the area of the brain tumor. The experiment results show that the enhancing process strengthens the features of tumor greatly, and improves the contrast and definition of the image.