Foldable air duct extension device

The utility model relates to the field of cavern blasting, and discloses a foldable air duct extending device which comprises a sliding telescopic rod arranged at the top of an excavated cavern, and the sliding telescopic rod comprises a sleeve section and a sliding section telescopically arranged in the sleeve section. The sliding telescopic rod is riveted and fixed to the top of the excavated cavern through rivets at the ends of the sliding section and the sleeve section. The sliding telescopic rod is sleeved with a plurality of sliding rings, and the folding air duct is hung on the sliding telescopic rod through the sliding rings; the folding air duct comprises a folding section and an extension section, and the extension section extends the length of the air duct by continuously increasing the number of pipe joints so as to be matched with the tunneling distance of a tunnel face. The distance between the folding air duct and the blasting tunnel face can be adjusted and changed, ventilation and exhaust of