The present invention discloses a combined flue gas exhaust pipeline comprising flue gas exhaust pipeline bodies which are mutually abutted together vertically. A convex block integrated with the inner wall of each flue gas exhaust pipeline into a whole is arranged on the inner wall of the flue gas exhaust pipeline; the outer end face close to the upper port edge of each flue gas exhaust pipeline body on the convex block is lower than the upper port edge at the end part of the flue gas exhaust pipeline body; the outer end face close to the lower port edge of each flue gas exhaust pipeline body on the convex block is higher than the lower port edge at the end part of the flue gas exhaust pipeline body; and a cavity at adjacent abutted position of the flue gas exhaust pipeline bodies is internally provided with a connecting piece which has adaptive shape with the cavity of the flue gas exhaust pipeline and is arranged between end faces of the convex block. Since the connecting piece is arranged at the direct abutted position of an upper flue gas exhaust pipeline and a lower flue gas exhaust pipeline, the flue gas exhaust pipeline can be arranged at any position of floor, and is convenient to construct, install, hoist and transport with high construction efficiency.