The invention relates to an underwater charging device for a submersible vehicle and a realization method thereof. The underwater charging device comprises a charging base module, wherein the chargingbase module is of a right angular structure; a charging socket and a steel wire rope connector are arranged at the inner side of the vertical right angle edge of the charging base module; a chargingclamp module is arranged on the horizontal right angle edge; the charging clamp module is connected with the steel wire rope connector on the charging base module through the steel wire rope; a hydraulic locking mechanism is arranged inside the charging clamp module; meanwhile, a charging connector module is also arranged inside the charging clamp module; the head part of the charging connector module is connected with the charging socket. The underwater charging device has the advantages that the structure is compact and reasonable; the operation is convenient; an ROV is arranged through a nuclear power submersible vehicle; the underwater charging device is operated to charge the conventional submersible vehicle under the water; the underwater operation duration of the submersible vehiclecan be effectively prolonged; the submersible vehicle exposure rate is reduced; the execution of invisible operation tasks by the submersible vehicle is facilitated.