Abstract: For underwater maintenance requirement of spent fuel pool cladding plate in nuclear power plant, the tests of underwater local dry laser welding drainage process of S32101 dual-phase stainless steel were carried out. The underwater local dry welding drainage process was optimized by changing the drainage gas flow rate. The drainage gas flow rate of 40-50L/min is better, which could effectively isolate the influence of hydrogen and oxygen elements in the water environment on the weld forming process. The same welding process parameters were used in the air and underwater environments for bevel welding filler test, and the surface forming, microstructure and properties of the welds in the two environments were compared and studied. The results show that the inert gas inflatable drainage is used to form a good protective gas atmosphere in the welding area, which effectively isolates the harmful elements in the air from invading the weld, and the oxidation degree of the weld surface formed in underwater is reduced. The austenite content of the welds in the two environments is similar, but the underwater cooling effect causes precipitation of a larger number of γ₂in the weld microstructure. Through tensile, bending,impact performance tests, the performance of the welded joint obtained in underwater environment can be comparable to that of the welded joint in air environment.