Abstract: Weld is the main way of constructing steel structure.X ray detection is one of the few major techniques in detecting weld defects.There are two methods for evaluating the results of X ray detection: manually and automatically evaluation.In a manual way,the person may be tired so the result is not reliable,and the evaluation is subjective.The computer aided analysis and recognition can improve the efficiency.The basis of analysis and recognition is image segmentation.This article is based on CV model which is an development of Mumford-Shah model and active contour by Tony,Chan and Luminita.And we apply this model in welding seam defects detection.