The invention discloses a support device for a B type enclosure system of a large LNG carrier. The support device comprises a first cylinder bearing wood and a second cylinder bearing wood; the secondcylinder bearing wood is arranged on the periphery of the first cylinder bearing wood in a sleeving mode to form a supporting main body, and the upper end face of the supporting main body is providedwith an upper panel and the lower end face of the supporting main body is provided with a lower panel; an upper part criss-cross bracket plate is arranged on the upper surface of the upper panel, anda lower part criss-cross bracket plate is arranged on the lower surface of the lower panel; and an upper part support circular ring and a lower part support circular ring are separately arranged on the outer wall of the second cylinder bearing wood, an upper part circular ring bracket plate is arranged on the outer side of the upper part support circular ring and is fixed on the lower surface ofthe upper panel, and a lower part circular ring bracket plate is arranged on the outer side of the lower part support circular ring and is fixed on the upper surface of the lower panel. The support device for the B type enclosure system of the large LNG carrier is simple to manufacture and easy to install, and the supporting main body can simultaneously transmit loads in the vertical and horizontal directions and can withstand any load in the horizontal direction, so that the action of rolling and pitching is prevented.