The utility model provides a body centre bore sealing device is set to horizontal production tree under water, including last body, lower body component device body, forming the mandrel by last mandrel, lower mandrel, during the mandrel penetrated the coaxial centre bore of body, lower body, upward fixeing jacket encircled outside the body, and the outer lantern ring and last body outer wall formation annular groove set up the sealing ring in, the interior lantern ring is established to the cover on the mandrel, and the interior lantern ring is placed in go up setting one's heart the shaft seal circular bead and between the bottom centre pillow block of mandrel is takeed on down, being connected through fastening screw of mandrel between the interior lantern ring and the sealing ring, body top interval bottom the outer lantern ring is relative down, and rubber seal is established to the interval cover, and the sealing ring upper portion outside sets up the bulge, and sealing washer inner wall extension extremely in the annular groove, the utility model discloses an expandable sealing that the operation realized production tree body centre bore is put through simple hoist and mount, centering, seat to sealing device, has reduced underwater operation's the degree of difficulty, practices thrift underwater operation's time and cost.