The invention provides an emergency floating load rejection system of a manned underwater vehicle. The emergency floating load rejection system comprises a ballast mechanism, a limiting mechanism, anelectric release mechanism and a manual release mechanism, wherein the ballast mechanism comprises a weight cabin which contains weights, and a movable door capable of rotating is arranged at the bottom of the weight cabin; the limiting mechanism is arranged at the position of the movable door and is used for limiting the movable door, and comprises a lever and a locking rod, wherein the lever ishinged to the movable door, and the locking rod abuts against the lever; the electric release mechanism and the manual release mechanism are two parallel ways for opening the movable door, and the twoways are independent and mutually backed up, so that the overall reliability of the system is greatly improved; meanwhile, traditional exploding, electromagnetic and electrochemical modes and other modes are abandoned, safety and maintainability are greatly improved, and the technical problem that the starting mode of a traditional load rejection system is single is solved.