Abstract: In order to realize the underwater in-situ repair of the upper core plate locating pin, this paper conducted the underwater local dry TIG welding process of 304 stainless steel, and analyzed the influence of welding process parameters on welding quality. The test results show that the shape of the weld joint obtained by underwater welding of the positioning pin simulator is good, and there are no significant oxidation and surface defects. With the increase of welding current and welding time, the cross-section size of the solder joint also increases significantly, resulting in the gradual increase of the compression property of the solder joint. The weld area of the welding spot is composed of γ-Austenite and a small amount δ-Ferrite. Grain coarsening in the heat affected zone due to thermal cycling also existed. Considering the welding efficiency and mechanical properties of the solder joint, No.2 welding process parameters can realize the high-quality joining of the locating pin simulated sample, which is of great significance for underwater welding maintenance.