An automatic removal device for an underwater mooring chain comprises a shackle (101), and a link (103) connected to a recess (102) inside the shackle (101). A side wall of the shackle (101) is further provided with a fixing structure (1). The link (103) is connected to the fixing structure (1) and the shackle (101) via a removable structure (2). A sliding connecting structure is arranged between the fixing structure (1) and the removable structure (2). When used in a deep water area, the removable structure (2) is grasped by a ROV robot, so as to release the link (103). When used in a shallow water area, the removable structure (2) can be controlled by a ROV robot and manual control, so as to release the link (103). The invention is easy to operate, achieves effective replacement, and is safer and more reliable.