In casting defect recognition of an X Ray image，due to the complex image background，it is difficult to do segmentation with traditional segmentation technology for interested regions，in which the defects are intense. In this paper，fractal feature of the edges is introduced to distinguish which edge belongs to the casting defects in an edge image and the regions containing mass defect edges，e.g. interest regions are segmented by clustering. Directed to the aluminum alloy casting of vehicle wheel X Ray images，the fractal based region segmentation method of this paper is used for recognition experiments，and the results show that the approach is effective.