NOVELTY - Producing biological methane, comprises: e.g. (a) placing cassava dregs and alcohol waste liquid into baffle depositing pool, removing large grains from the materials to adjust solid liquid ratio and pH value; (b) conveying material into hydrolysis acidification pool for hydrolysis and acidification, and converting residual starch, protein, cellulose and sugar of cassava dregs and alcohol waste liquid into organic acid; and (c) pumping the materials into adjusting pool and then mixing return sludge of anaerobic reactor and sedimentation tank, water, buffer solution and strains,    USE - The method is useful for producing biological methane, which is useful as fuel gas for motor vehicle (claimed).    ADVANTAGE - The method allows easy and economical production of the biological methane with high efficiency and quality and improved yield in an environmentally friendly manner.    DETAILED DESCRIPTION - Producing biological methane, comprises: (a) placing cassava dregs and alcohol waste liquid into a baffle depositing pool, removing large grains from the raw materials, and adjusting a solid liquid ratio and a pH value of the materials; (b) conveying the material into a hydrolysis acidification pool for hydrolysis and acidification, and converting the residual starch, protein, cellulose and sugar of the cassava dregs and alcohol waste liquid into low-molecule organic acid; (c) pumping the materials into a adjusting pool after the acidification reaches a peak value, uniformly mixing the materials with return sludge of the anaerobic reactor, return sludge of sedimentation tank and water in the acidification pool, buffer solution and strains; (d) introducing the mixture into an anaerobic fermentation tank to ferment, where in the fermentation tank, the anaerobic microorganism to organic substance in the sewage or sludge are decomposed into the methane and carbon dioxide, the sludge is settled and dried to serve as biological fertilizer, the sewage is completely aerated in the aerobic tank and the residual organism is degraded so as to be discharged after the chemical oxygen demand reaches the standard; and (e) collecting obtained biological methane, storing the methane at a concentration of 55-65% to a wet gas storage cabinet, directly conveying the gas to a boiler workshop to serve as fuel, conveying the other methane to a fuel gas workshop for purification, collecting the purified gas after the methane concentration is 97% into an independent gas cabinet, and compressing and conveying the purified gas to a refueling station to serve as fuel gas for the motor vehicle.