NOVELTY - The method comprises dewatering biological sludge, pre-storing the dewatered sludge in a storage chamber, preheating the dewatered sludge in a preheating system, heat treating in a hydrothermal reactor to obtain hydrothermal cracking liquid, passing the hydrocracking fluid to a preheating pipe to obtain a lysis solution and a gas product, passing the hydrothermal cracking solution into a filter press, obtaining the reaction liquid with a solid product, and drying the solid product in a dry carbonization furnace to obtain solid biological carbon and other products.    USE - The method is useful for carbonization of biological sludge by hydrothermal reaction (claimed).    ADVANTAGE - The method ensures carbonization of the biological sludge with high efficiency and less consumption of energy.    DETAILED DESCRIPTION - The method comprises dewatering biological sludge, pre-storing the dewatered sludge in a storage chamber, pre-heating the dewatered sludge in a preheating system, heat treating in a hydrothermal reactor to obtain hydro-thermal cracking liquid, passing the hydrocracking fluid to a preheating pipe to obtain a lysis solution and a gas product, passing the hydrothermal cracking solution into a filter press, obtaining the reaction liquid with a solid product, drying the solid product in a dry carbonization furnace to obtain solid biological carbon and other products, introducing other products into a gas-liquid separating device for separating the gas and tar, adding the combustible gas and tar into a combustion chamber to generate heat energy, and providing the heat energy to a hydrothermal reactor with a dry carbonization furnace. The water content of the dewatered sludge is 70-85 wt.%. The preheating system is operated at 110-180 degrees C. The hydrothermal reactor is operated at a temperature of 200-300 degrees C for 30-90 minutes and at a pressure of 3-10 MPa for heat treating the dewatered sludge. The preheating pipe is equipped with a back pressure valve. The water content of the obtained solid product is 30-40 wt.%. The solid product is naturally dried and aerated to the water content of 10-30 wt.%. The hydrothermal reaction is carried out at a temperature of 500-700 degrees C for 30-60 minutes.