NOVELTY - Anaerobically digesting sludge, comprises conditioning sludge using physical method or chemical method, conveying the sludge to a completely mixed in an anaerobic digestion tank and then pneumatic stirring, or intermittent mechanical stirring, mixing the stirred mixture into a sludge tank, carrying out anaerobic digestion to generate anaerobic digestion liquid, collecting methane-containing biogas in a marsh gas tank and then dehydrating, desulfurizing and decarbonizing treatment in the anaerobic digestion process, and separating the biogas residue into a flow reactor.    USE - The method is useful for anaerobically digesting sludge (claimed), which is useful in agricultural and other fields.    ADVANTAGE - The method is capable of conveniently digesting the sludge with high marsh gas production rate.    DETAILED DESCRIPTION - Anaerobically digesting sludge, comprises conditioning sludge (90-92%) using physical method or chemical method, where the sludge has a carbon nitrogen ratio of 10-20, and a pH value of 6.5-7.5, conveying the sludge to a completely mixed in an anaerobic digestion tank at a temperature of 35-37 degrees C, controlling the partial temperature of the sludge to plus minus 0.5 degrees C and then pneumatic stirring, or intermittent mechanical stirring at a speed of 60 revolutions per minute (rpm), mixing the stirred mixture into a sludge tank, carrying out anaerobic digestion for 15-20 days to generate anaerobic digestion liquid, collecting methane-containing biogas (60-70%) in a marsh gas tank and then dehydrating, desulfurizing and decarbonizing treatment in the anaerobic digestion process, separating the biogas residue (50-70%) into a flow reactor and then carbonizing and discharging, separating the carbonized residue using wooden meal or waste paper according to a mass ratio of the 1:3-10 and then directly mixing and carbonizing in carbonization device to obtain biogas residue (20-30%), anaerobically or anoxically reacting the biogas residue for 10-20 minutes to obtain biological carbon particle, directly conveying the biological carbon particle to a combustion chamber at a high temperature and pressure and then continuously carbonizing through a pipeline to supply heat for carbonization reaction at a 600-800 degrees C and a pressure of 15-16 MPa.