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 buildup 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.