To improve the welding quality of the locally drying underwater SMAW,develops a new device in the locally drying underwater SMAW and carry out a lot of systematic technology experiments. By the experiments,we finally get such results:the structure of the device is simple,the welding formation is well. Compared to the drying welding,the penetration improves a lot in the welding and the weld width decreases a little under the water,because of compression of the arc by gas. With the increase of water depth,the gas pressure increases accordingly,the penetration improves and the weld width decreases further. In addition the transition between weld and base metal is more smooth,and this reduced stress concentration.