The invention relates to a seabed negative electrode of a seabed single-electrode direct current power supply system, and belongs to the technical field of power supply. The seabed negative electrode comprises an electrode body and a watertight connector electrically connected with the electrode body; the electrode body comprises a tetrahedron-shaped rod-like structure formed by six body titanium rods in a surrounding manner and an anti-collision apparatus arranged on the periphery of the watertight connector; and the anti-collision apparatus is fixedly arranged on one top corner of the tetrahedron-shaped rod-like structure. By setting the seabed negative electrode into the tetrahedron-shaped rod-like structure, the anti-collision performance and anti-burying performance in the use process can be effectively improved, thereby effectively ensuring the normal operation of the seabed single-electrode direct current power supply system constructed by the seabed negative electrode; and therefore, the seabed negative electrode can be widely applied to the seabed power supply technical fields, such as a seedbed observation network and the like.