NOVELTY - An animal waste is purified through a roller oscillating sieve. The purified animal waste is conveyed to a waste accumulating pool, and water is added. Then, the diluted animal waste is conveyed to a cultivation pool. Waste liquid or active sludge is added, cultivated, and conveyed to an anaerobic fermentation tank (A1). The cultivated waste liquid or active sludge in the anaerobic fermentation tank (A1) is slowly heated to 56 degrees C or less, and acid degradation is processed for 4-6 hours. The generated biogas is put in a carbon-steel sealing bottle or jar.    USE - Method for preparing biogas used for organic fertilizer using animal waste as raw material through high temperature anaerobic fermentation.    ADVANTAGE - The preparation method of biogas is economical, eco-friendly and efficient. The waste heat generated in the method is utilized.    DETAILED DESCRIPTION - An animal waste is purified through a roller oscillating sieve. The purified animal waste is conveyed to a waste accumulating pool, and water is added for dilution. The pH value is controlled to 7.1-7.5. Then, the diluted animal waste is conveyed to a cultivation pool or an incubation bed, and temperature is controlled at 28-32 degrees C. Waste liquid or active sludge perennially aggregated on farm is added, cultivated for 10-30 days, and conveyed to an anaerobic fermentation tank (A1). The cultivated waste liquid or active sludge in the anaerobic fermentation tank (A1) is slowly heated to 56 degrees C or less, and acid degradation is processed for 4-6 hours. The water pump is circulated, the temperature rise and circulation is stopped at 58 plus minus 1 degrees C, and temperature is kept constant for 24 hours. The generated biogas is put in a carbon-steel sealing bottle or jar. A pump is used to pump the feed liquid to an anaerobic fermentation tank (A2). The feed liquid in the anaerobic fermentation tank (A2) is slowly heated to 56 degrees C or less, and acid degradation is processed for 4-6 hours. The water pump is circulated, the temperature rise and circulation is stopped at 58 plus minus 1 degrees C, and temperature is kept constant for 24 hours. The generated biogas is put in a carbon-steel sealing bottle or jar. A pump is used to pump the feed liquid to an anaerobic fermentation tank (A3). The processes carried out in the anaerobic fermentation tanks (A1,A2) are carried out in the anaerobic fermentation tank (A3). Then, a pump is used to pump the feed liquid to an anaerobic fermentation tank (A4). Then, the liquid is put to jar of the anaerobic fermentation tank (A1) after maintaining at constant temperature for 24 hours. Similarly, the liquid is put into fermentation tanks (A8-A30), and temperature is kept constant for 24 hours. The generated biogas is put to the carbon-steel sealing bottle or jar, and washed with water. The biogas is put in a desulfurizing tower, and desulfurized. The desulfurized biogas is dried in a drying tower, and put into an air holder. The feed liquid is put into a fully automatic drug liquid centrifugal dehydration pump, and separated. The separated biogas drug is added to an automatic dosing tank, put into an organic fertilizer pellet production line, put for secondary parching after pellet cooling and encapsulated to obtain an organic solid fertilizer. The biogas liquid is separated in the liquid centrifugal pump, settled in a sedimentation tank, and an organic condensed fertilizer is obtained.