Abstract: Due to the relatively large gas space and better flexibility, chamber local dry underwater welding has a better application prospect in repairing offshore gas and oil pipeline and nuclear spent fuel pool. With the development of chamber local dry underwater welding system, the verification test of buildup welding and butt welding were conducted in a 300 mm depth water environment, and the microstructure and hardness of butt weld were analyzed. The results show that with the premise that the chamber was well sealed, the wire feed speed, welding speed, weaving speed and weaving period have a great influence on the weld formation and welding quality. By optimizing different welding parameters, a good appearance of chamber local dry underwater welding weld can be obtained; Underwater welding environment has influence on hardness and microstructure of weld; Due to the rapid cooling effect of water back and around the weld, some widmanstatten structure appear in the center region of the weld, the hardness in the central region is higher than that in the heat affected zone and, hardening phenomenon appeared.