Abstract: EH36 steel is one of the steels commonly used for underwater structures. To investigate the adaptability of EH36 steel to underwater local dry arc additive manufacturing, an underwater local dry arc additive manufacturing experimental platform was established, and comparative experiments of on-land and underwater local dry arc additive manufacturing were conducted. The forming accuracy, microstructure, tensile strength, impact toughness, and corrosion resistance of the EH36 steel single-wall additive specimens under the two conditions were obtained and compared. The results indicate that the forming accuracy of the underwater local dry arc additive manufacturing specimens is slightly lower under the same welding process parameters. Due to the water cooling effect, less proeutectoid ferrite is formed at the bottom of the underwater single-wall; grain growth is inhibited in the middle to form fine-grain strengthening; lath martensite is formed at the top. The strength of the underwater additive specimens is higher, but the toughness is slightly decreased. The results of tensile strength, impact toughness, and corrosion resistance tests show that the mechanical properties of the single-walls under the two environments have little difference; the corrosion resistance of the underwater local dry arc additive manufacturing specimens is slightly inferior to that of the on-land specimens. Overall, the performance of the underwater local dry arc additive manufacturing specimens is comparable to that of the on-land specimens, indicating that this method can serve as a convenient and efficient underwater additive repair method.