Welding is a common process in the construction of water conservancy and hydropower projects. In the common welding and production process, carbon steel castings occupy a considerable proportion. After carbon steel castings are processed, various defects often appear on their surfaces, such as cracks, sand holes, air holes and other casting defects, which directly affect the final service life and surface quality of products, so it is necessary to repair them. At this point, because the size of each part of the part has been processed, the defects of the part are difficult to repair. In the past, we used the process of surfacing welding in a large area first and then reprocessing on the machine tool, which not only caused a great waste of machine time, but also caused obvious convex weld marks in the reprocessing due to the hardening tendency caused by the accumulation of carbide in the base material and welding repair. At the same time, when repairing defects, it is often because of incomplete grinding and other reasons that welding can not be completed at one time. After reprocessing, the original sand holes and air holes will be exposed again, and the effect is not ideal, which leads to many products leaving the factory with defects and causes serious losses to the company's economy and reputation.