Abstract: In order to overcome the difficulty of wet-type underwater electrode welding, a novel p semi-dry type underwater overhead welding was proposed. The principle of the process and the operation procedure was clarified it's the welding ability, weld microstructure, hardness and diffusion hydrogen content were studied. The results indicate that this semi-dry overhead welding procedure can be successfully applied in underwater overhead welding position and the appearance of weld is good. The optimum welding current range is 100-140 A for electrode of Φ3.2 mm diameter, the corresponding welding voltage range is 28-32 V. The weld microstructure is mainly composed of ferrite side-plate, needle-like ferrite and bainite. Compared with the traditional underwater wet-type welding, the content of ferrite increased, and the content of bainite decreases accordingly. The highest hardness of welded joints and diffusion hydrogen content in deposited metal are remarkably lower than those of the wet-type underwater electrode welding.