NOVELTY - The anaerobic fermentation system comprises a pre processor device for separating solid and liquid from farm, food and agricultural by-products and organic waste when supplying with high concentration of solids in liquids. An aerobic fermentation tank ferments the separated solids received from the pre processor by supplying aerobic microorganisms. An anaerobic fermentation tub comprises a sealing closure with a gas-storage tank, and produces the methane gas by fermenting the waste in the sealed interior volume of the sealing closure.    USE - The anaerobic fermentation system is useful for fermenting farm, food and agricultural by-products and organic waste and for producing methane gas (claimed), and liquefied fertilizer.    ADVANTAGE - The system can rapidly ferment the wastes in a convenient and safe manner without the inflow of oxygen, and produces the methane gas in an effective manner.    DETAILED DESCRIPTION - The anaerobic fermentation system comprises a pre processor device for separating solid and liquid from farm, food and agricultural by-products and organic waste when supplying with high concentration of solids in liquids. An aerobic fermentation tank ferments the separated solids received from the pre processor by supplying aerobic microorganisms. An anaerobic fermentation tub comprises a sealing closure with a gas-storage tank, and produces the methane gas by fermenting the waste in the sealed interior volume of the sealing closure. A mixer comprises: a driving carriage that is arranged in an upper side of the aerobic fermentation tank along a rail of the aerobic fermentation tank; an agitating blade with a first motor; and a roller rotated by a second motor in the aerobic fermentation tank. The agitating blade is movably installed at the carriage, and mixes the solid material within the aerobic fermentation tank. The pre processor comprises a liquid bath that is connected a liquid transfer pump and a piping network to supply a hydraulic liquid to the anaerobic fermentation tub. The hydraulic liquid piping network is fixed at a lower part of a framework of the pre processor. A mixing apparatus is arranged in a bottom surface of the pre processor. A rotating blade is arranged in a guide rail formed on a horizontal frame of the framework. A solid-liquid separation tank includes a vent for inputting the waste within the aerobic fermentation tank. An overflow pipe is equipped in an overflow liquid storage tank. An INDEPENDENT CLAIM is included for a method for fermenting farm, food and agricultural by-products and organic waste.