After analyzing the factors which affect the technology of single electric three-wire submerged arc welding,and comparison of physical and chemical properties of weld metal with single wire and double wire submerged arc welding and its weldability test,it is found that the physical and chemical properties of weld metal by single electric three-wire submerged arc welding meet the requirements of ASME BPVC. Ⅷ.2. Meanwhile,when the total heat input is constant,the addition of cold wire can reduce the heat which transferred to the base metal,improve the microstructure and properties of the welded joint,enhance the welding deposition rate. The technology of single electric three-wire submerged arc welding can be widely applied to welding parts such as support boss and big triangle weld of skirt in the hydrogenation reactor.