The utility model relates to a sealer for an orifice of a furnace tube. The furnace tube is a core part of a converter furnace of a methanol device. The sealer comprises a bottom layer board, a compression plate, at least two columns, a branch pipe table and an emptying pipe, wherein the bottom layer board is used for being contacted with the outer wall of the furnace tube on the lower part of the orifice; the compression plate is contacted with the upper part of the orifice; the columns pass through the bottom layer board and the compression plate so as to apply clamping forces to the bottom layer board and the compression plate; the branch pipe table is arranged on the compression plate and embedded into the orifice; and the emptying pipe is connected with the branch pipe table and used for emptying air in the furnace tube. According to the sealer, an orifice sealing process of a welded blind plate in the prior art is changed to mechanical tool sealing, so that the construction cost is lowered, the labor intensity is alleviated, and the construction efficiency is improved by over 200%.