The invention belongs to the technical field of ship body structures, and discloses a ship body double-layer bottom structure and an installation method thereof, in the installation process of the ship body double-layer bottom structure, when a worker assembles an inner bottom plate body, a ship outer plate, a
solid rib plate and a rib, installation of a slow-installation cover plate can be delayed, and when the structure is assembled, installation of the slow-installation cover plate is facilitated. In addition, after installation of the inner bottom plate body, the ship outer plate, the
solid rib plate and the ribs is completed, a worker can also firstly install other equipment in the
bilge of the ship body, due to the fact that the slow installation cover plate is not installed yet, the large operation space is achieved at the moment, and after installation of the structure is completed, the worker can conveniently install the inner bottom plate body, the ship outer plate, the
solid rib plate and the ribs. The buffer cover plate is installed in the containing groove and fixedly connected with the ship outer plate, the groove wall of the containing groove, the solid rib plate and the ribs at the same time, due to the fact that the surface of the buffer cover plate is flush with the surface of the inner bottom plate body, the space above the inner bottom plate cannot be occupied, and more installation space can be reserved for a
liquid tank or cabin equipment.