The invention relates to a thermal insulation sealing device for a manhole of a stirred tank. The sealing device is characterized by comprising a sealed barrel, thermal insulation rock wool, a cross beam slide rail, a hanging block, a pulley, a hanging rod and a sealing flange, wherein the thermal insulation rock wool is filled in the sealed barrel; the upper end of the hanging block is hung on the cross beam slide rail through the pulley, and the lower end of the hanging block is connected with the upper end of the hanging rod and is connected with the upper end of the sealing flange; the sealing flange is fixedly connected with one end of the sealed barrel. The device has the advantages that material accumulation at a manhole cylinder section can be prevented and a thermal insulation effect is realized.