A heat exchange flue, having a top flue gas chamber (1), a bottom flue gas chamber (10) and a heat exchange section (H) located therebetween. The heat exchange section (H) comprises a heat exchange tube bundle (4) located in the middle, and a left side flue (5) and a right side flue (12) which are located at two sides of the heat exchange tube bundle (4). The axis of the heat exchange tube bundle (4) is positioned in a vertical plane extending substantially forward and backward, allowing the flue gas to laterally flush against the surfaces of heat exchange tubes. The left and right side flues (5, 12) are in a vertical box shape, the flues are each provided with a plurality of flue gas dampers (3) which are vertically arranged at intervals in a substantially horizontal alignment. Each of the flue gas dampers (3) is provided with a flue gas damper frame (13) for defining a flue gas port (2) and a flue gas port opening/closing device capable of selectively opening and closing the flue gas port (2). The flue gas damper frames (13) are hollow out and horizontally arranged, and have an outer contour consistent with the sectional shape of the left and right side flues (5, 12), the peripheral edges thereof are respectively connected to a peripheral flue gas wall in an airtight manner, and the parts thereof corresponding to the heat exchange tube bundle (4) are connected to a substantially horizontal flue gas shield plate (6) in an airtight manner. The flue structure can adjust the working load to the greatest extent to ensure the flue gas temperature and prevent condensation.