NOVELTY - Producing methane using tower-type large capacity dual fermentation system, comprises (i) pouring fermentation raw material feedstock into an intermediate cylinder of a first-stage fermentation system, and pouring feedstock into a second-stage fermentation system by using a feeding tube; (ii) allowing the production of biogas; (iii) carrying out secondary fermentation; (iv) storing biogas in a storage chamber under water pressure conditions; (v) storing the secondary fermentation biogas through a pipeline into a reflux device-containing slurry; and (vi) repeatedly producing biogas.    USE - The method is useful for producing methane using tower-type large capacity dual fermentation system (claimed).    DETAILED DESCRIPTION - Producing methane using tower-type large capacity dual fermentation system, comprises (i) pouring fermentation raw material feedstock into an intermediate cylinder of a first-stage fermentation system, and then pouring fermentation raw material feedstock into a second-stage fermentation system by using a feeding tube; (ii) allowing the production of biogas during the fermentation stage in the fermentation system, where the biogas accumulates in an inlet and an outlet along the side walls of the cylinder and adjacent to an air resistant plate or accumulates between the adjacent air resistance plates in a fermentation area, and extruding the fermentation slurry through a third-level fermentation pipe, and allowing the fermentation slurry to flow into second-stage fermentation system by third-level fermentation pipe under pressure, once the slurry in the third-level fermentation pipe increases; (iii) carrying out secondary fermentation to produce biogas in the fermentation system, and allowing biogas to accumulate in a secondary inlet/between the side walls of a discharge tube and along the adjacent side of air resistant plate or to accumulate between adjacent air resistant plates in the fermentation area, extruding the biogas inside the tubes to allow to flow into 2 feeding tubes, and draining from two feeding tubes into bacterium-based fabrics, and passing through bacterium-based fabrics under pressure; (iv) storing biogas in a storage chamber under water pressure conditions, and passing through a fourth-level fermentation pipe, once the primary fermentation of biogas is complete; (v) storing the secondary fermentation biogas through a pipeline into a reflux device-containing slurry, and storing in bacterium-based fabric under pressure passed through secondary fermentation pipeline; and (vi) repeatedly producing biogas.