The invention discloses an underwater tree cap feeding tool. The underwater tree cap feeding tool comprises a tool body, a drive connection mechanism and a connection and separation mechanism; an overall shape of the tool body is of a cylindrical structure, and the top of the tool body in the height direction is a connecting part for being connected with a drill rod; the drive connection mechanismis installed at the middle part of the tool body in the height direction in a sleeving mode, the drive connection mechanism is used for driving an actuation ring of an underwater tree cap, so that the underwater tree cap is connected with an underwater horizontal type Christmas tree in a locked mode; the drive connection mechanism includes an actuating piston, a piston driving structure and a temporary limiting structure before driving; the connection and separation mechanism is installed at the bottom part of the tool body in the height direction in a sleeving mode, and the connection and separation mechanism is used for connecting with or separating from the underwater tree cap; and the connection and separation mechanism includes a lower baffle ring, a locking ring, a drive ring, and adriving structure for the drive ring. The underwater tree cap feeding tool has the advantages of simple structure, reliable performance and convenient use, and is suitable for being popularized and used.