Image Processing of wood defects is important for wood defects recognition. Wood defects influence on wood production quality. X-ray testing system was adopted to detect wood defects. Because it not only can detect wood seeming defects, but also can detect inner defects. The collected images with defects were done median filter processing and edge detection so that the position, size and shape of wood defects are obvious in images. The experimental results show that the results of image processing can recognize wood defects effectively. This method not only provides reliable evidences for features extraction of wood defects, but also it lays a foundation for automatic recognition. It is helpful for wood reasonable selection and scientific utilization.