The invention discloses a marine inclined ladder door/cover, and belongs to the technical field of ships. The marine inclined ladder door/cover is mounted between an upper deck and a lower deck, and characterized by comprising a ladder assembly; the ladder assembly comprises a bottom ladder frame and a surface ladder frame which are parallel to each other; multi-stage parallel steps are vertically hinged between the bottom ladder frame and the surface ladder frame; the top end of the ladder assembly is hinged to the upper deck; the bottom end of the ladder assembly is propped against the lower deck; the ladder assembly can upwards rotate around the hinge point between the ladder assembly and the upper deck to seal the opening of the upper deck. The marine inclined ladder door/cover is simple in structure, convenient to operate and dual in purpose, and has the advantages that not only can people on a ship be protected when necessary, but also additional building cost is avoided.