NOVELTY - A cylindrical device for continuously producing methane by two-stage fermentation comprises an outer cylinder (12) with two closed ends and a U-shaped groove (14) positioned in the inner chamber of the outer cylinder (12); where the walls of the two sides of the U-shaped groove (14) have a height difference; the higher wall of the U-shaped groove (14) is fixedly connected with the outer cylinder (12) and set with a vent (4); and the outer cylinder (12) is set with a feeding opening (10) which is at the outer side of the higher wall of the U-shaped groove (14).    USE - The cylindrical device is useful for continuously producing methane by two-stage fermentation (claimed).    ADVANTAGE - The cylindrical device can separate the methane materials for generating gas from the methane materials to be fermented to continuously generate gas via two-stage fermentation; where the utilization rate of the methane material is increased. Moreover, the external hot water can be brought in for heating the methane liquid, which solves the problem that the methane liquid cannot generate gas due to low temperature. Additionally, the device has simple structure, low manufacturing cost, convenient material feeding and discharging, and simple operation.    DETAILED DESCRIPTION - A cylindrical device for continuously producing methane by two-stage fermentation comprises an outer cylinder (12) with two closed ends and a U-shaped groove (14) positioned in the inner chamber of the outer cylinder (12); where the walls of the two sides of the U-shaped groove (14) have a height difference; the higher wall of the U-shaped groove (14) is fixedly connected with the outer cylinder (12) and set with a vent (4); the outer cylinder (12) is set with a feeding opening (10) which is at the outer side of the higher wall of the U-shaped groove (14); the U-shaped groove (14) is connected with a discharging opening (1) arranged on two end faces or bottom of the outer cylinder (12); the outer wall of the outer cylinder (14) is set with a rotary handle (13); and the outer cylinder (12) is supported by a rolling wheel (16) installed on the pedestal (17).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the cylindrical device for continuously producing methane by two-stage fermentation.    Discharging opening (1)    Outlet interface (3)    Vent (4)    Temperature sensor (8)    Hot water inlet interface (9)    Feeding opening (10)    Outer cylinder (12)    Rotary handle (13)    U-shaped groove (14)    Hollow heating tube (15)    Rolling wheel (16)    Pedestal (17)