Abstract: It is useful for determining the discontinuities harmfulness to welds, and is especially important for repair if the discontinuities in the welds were precisely located. When examining by RT method to test the welds quality, the author find a method to locate discontinuities position from RT film. According to different welding process we can analyze the reason that discontinuity occurs, the shape of discontinuity and the type of discontinuity. The analysis was based on welding groove angle, welding pass and on whether the welding being one side with back formation or two side. At the same time, through using sample film and film darkness scan the welding seams could be divided into three categories, lower, middle and upper tier. And hence the discontinuity could be positioned and its height be estimated, thus mostly meeting the needs of repair location and figuring out whether the discontinuity is harmful or not. And this has good results in practice.