The invention relates to an ascending flue. The ascending flue comprises a smoke pipe, wherein an outer ring steel plate is arranged on the pipe wall at the upper part of the smoke pipe, an inner ringsteel plate is arranged on the inner side of the outer ring steel plate, and a smoke pipe groove is formed between the outer ring steel plate and the inner ring steel plate; the smoke pipe groove isfilled with refractory fibers, a butterfly valve is arranged in a smoke pipe smoke outlet cavity, and a cover plate is arranged at the top of the smoke pipe; the structure of the cover plate is characterized in that a top plate supporting steel plate is arranged on the outer circle below the top plate, a top plate outer ring steel plate is arranged on the inner side of the top plate supporting steel plate, a top plate inner ring steel plate is arranged on the inner side of the top plate outer ring steel plate, and a cover plate groove is formed between the top plate outer ring steel plate andthe top plate inner ring steel plate; and when the cover plate covers the smoke pipe, the top plate supporting steel plate is pressed on the outer ring steel plate of the smoke pipe to form a first-stage sealing ring, and the top plate outer ring steel plate is arranged in the center of the smoke pipe groove to form a second-stage sealing ring. The ascending flue has the advantages that cold air can be prevented from leaking into the annular flue basically, the energy consumption and the power consumption of a roasting section can be greatly reduced, and the operation cost of roasting purification is reduced.