NOVELTY - Fermenting excess sludge, by feeding a excess sludge from a sedimentation tank into a preprocessor of the sludge through a sludge conveying pipe, thermally pre-treating the excess sludge to inhibit the activity of the methanogen, mixing the excess sludge with the pre-treated sludge in the preprocessor of the sludge, cooling the mixed sludge, subjecting mixed sludge with the pH adjusted into a sealed internal circulation anaerobic reactor, and performing anaerobic fermentation for the mixed sludge to prepare hydrogen and methane.    USE - The method is useful for fermenting excess sludge for producing hydrogen and methane.    ADVANTAGE - The excess sludge of the sedimentation tank has a water content of 99% or more, and good liquidity hence the pipeline cannot be easily blocked. The method prevents pretreatment including blending operation of the sludge, and is simple to perform.    DETAILED DESCRIPTION - Method for fermenting excess sludge, involves (a) opening a first valve, closing a second valve, a third valve and a fourth valve, starting a first sludge conveying pump (1) to feed the excess sludge from a sedimentation tank into a preprocessor of the sludge through a sludge conveying pipe, closing the first conveying pump and the first valve, and thermally pre-treating the excess sludge to inhibit the activity of the methanogen on the basis of releasing the nutrition from the excess sludge at 60-80 degrees C for 15-30 minutes, (b) starting the first conveying pump, opening the first valve and pumping a certain amount of excess sludge, closing the first conveying pump and the first valve, mixing the excess sludge with the pre-treated sludge in the preprocessor of the sludge, cooling the mixed sludge to 50 degrees C or less, and adjusting the pH of the mixed sludge to 6.5-7.5, and (c) opening a second valve and a third valve, starting a second conveying pump to pump the mixed sludge with the pH adjusted into a sealed internal circulation anaerobic reactor (6), closing the second valve, the third valve and the second conveying pump, and controlling the anaerobic fermentation to 35 degrees C for performing anaerobic fermentation for 12-120 hours to prepare hydrogen and methane. An INDEPENDENT CLAIM is included for device for performing above-mentioned method, which comprises a sludge conveying pipe, first conveying pump, second conveying pump, first valve, second valve, third valve, fourth valve, pre-processor of sludge, sludge inlet (5), internal circulation anaerobic reactor, level-one three-phase separator (7), level-two three-phase separator, water discharge channel, gas-liquid separator (10), sludge discharge hole and a temperature control system, where the outlet of the first conveying pump is connected with the sludge conveying pipe, the outlet of the first conveying pump is connected with one end of the first valve through the sludge conveying pipe, the other end of the first valve is connected with the inlet of the pre-processor of the sludge through the sludge conveying pipe, the outlet of the pre-processor of the sludge is connected with one end of the second valve through the sludge conveying pipe, the other end of the second valve is connected with the inlet of the second conveying pump through the sludge conveying pipe, the outlet of the second conveying pump is connected with one end of the third valve through the sludge conveying pipe and the other end of the third valve is connected with a sludge inlet formed on the internal circulation anaerobic reactor, and the sludge discharge hole formed on the internal circulation anaerobic reactor is connected with one end of the fourth valve through the sludge conveying pipe, and the internal circulation anaerobic reactor is a sealed reactor installed with a temperature control system, the water discharge channel and a gas-liquid separator are arranged at the top of the internal circulation anaerobic reactor, level-one three-phase separator and a level-two three-phase separator are arranged inside the internal circulation anaerobic reactor and the level-one three-phase separator is placed under the level-two three-phase separator, the gas-liquid separator is connected with the level-two three-phase separator through a gas conveying pipe, and a sludge inlet and a sludge outlet are formed at the bottom of the reactor.    DESCRIPTION OF DRAWING(S) - The drawing shows schematic view of device for fermenting excess sludge.    Sludge conveying pipe (1)    Sludge inlet (5)    Internal circulation anaerobic reactor (6)    First-level three-phase separator (7)    Gas-liquid separator (10)