Abstract: Aiming at the facts that most X-ray digital images have the problem of low contrast, large background fluctuation and complex texture, b-spline curve is used to fit the column gray curves after preprocessing of weld images.The result shows that redundant curve peaks are eliminated and a smooth curve is abtained.Furthermore, curve extreme points are extracted and extreme value point set is modified twice by a fluctuation threshold and a boundary threshold.Finally, the shape and size of defects are revised by mathematical morphology and median filtering.Experiment results shows that this strategy effectively solves the problem of defect extraction caused by the weld seam with complex texture in X-ray image.It is advantageous to realize the automatic extraction of weld defects in X-ray image.