NOVELTY - Producing methane by multistage biogas fermentation system involves pouring fermentation material into a barrel shaped feed tube of secondary fermentation system (40). The biogas is collected in the space between the sidewall of the feedstock pipe(42) and the sidewall of the discharging pipe (44). The primary fermentation system generates and accumulate biogas in the fermentation space between the side wall of the discharging cylinder and the adjacent plate or between the adjacent blocking plates (43). The slurry is extruded in primary fermentation pipeline for flowing to first guide pipe.    USE - Method for producing methane by multistage biogas fermentation system (claimed).    DETAILED DESCRIPTION - Producing methane by multistage biogas fermentation system involves pouring fermentation material into a barrel shaped feed tube of secondary fermentation system. The biogas is collected in the space between the sidewall of the feedstock pipe and the sidewall of the discharging pipe. The primary fermentation system generates and accumulate biogas in the fermentation space between the side wall of the discharging cylinder and the adjacent plate or between the adjacent blocking plates. The slurry is extruded in primary fermentation pipeline for flowing to first guide pipe, second guide pipe and then to secondary fermentation pipe to generate and accumulate biogas in secondary fermentation pipe. The slurry is extruded in secondary fermentation pipeline for flowing to two grade feedstock tube, second level discharging pipe and drain pipe of the cloth bacteria device (70). The biogas is stored in two grade pipeline. The slurry is stored in water pressure chamber which returns through the cloth bacteria pipeline (74) device to secondary fermentation device.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of fermentation system.    Secondary fermentation system (40)    Feedstock pipe (42)    Blocking plates (43)    Discharging pipe (44)    Cloth bacteria device (70)    Cloth bacteria pipeline (74)