The invention belongs to the technical field of welding materials and discloses a self-protective flux-cored wire for all-position underwater wet welding in a deep water environment. The self-protective flux-cored wire comprises a metal skin and a flux core. The metal skin is formed by rolling an N6 nickel strip. The basic slag system of the flux core is an alkaline calcium fluoride-aluminum-magnesium slag system. The N6 nickel strip comprises, by weight, no smaller than 99.5% of Ni and Co in total, no larger than 0.06% of Cu, no larger than 0.10% of Fe, no larger than 0.05% of Mn, no larger than 0.10% of C, no larger than 0.10% of Si and no larger than 0.005% of S. The flux core comprises, by mass, 52-67% of fluoride, 14-20% of aluminum-magnesium alloy powder, 5-10% of calcium carbonate, 5-15% of ferromanganese, 3-10% of chromium, 4-10% of titanium and 1.5-5% of rare earth. The filling rate of the flux core in the flux-core wire is 24-32%. According to the scheme provided by the invention, the self-protective flux-cored wire can be used for welding under water by 100-200 meters, arcing is easy during welding, arc burning is stable, no arc blowout or breaking phenomenon occurs, an obtained welding seam is attractive in forming, the tensible strength of deposited metal after welding is larger than 500 MPa, and the self-protective flux-cored wire has good impact toughness and meets the all-position welding requirements of medium and low carbon steel and low alloy high strength steel in the deepwater environment.