Underwater repair in the original state is one of the preferred schemes for the spent fuel pool and in-containment refueling water storage tank of nuclear power plant. Using S32101 duplex stainless steel base metal and ER2209 stainless steel welding wire for the spent fuel pool of the third generation nuclear power plant, the experimental exploration of V-groove laser wire filling welding repair process is carried out, and the weld performance is comprehensively tested. The main conclusions include: the composite welding process of laser wire filling welding and laser reheating can obtain good weld formation, The weld structure is mainly composed of ferrite and austenite;According to the nuclear power construction standard, the room temperature tensile, high temperature tensile, low temperature impact, ferrite content and intergranular corrosion resistance of the weld meet the requirements; The research conclusions lay a good foundation for the research of underwater welding technology of spent fuel pool and in-containment refueling water storage tank in nuclear power plant.