NOVELTY - Sludge treatment based on hydrothermal modification method comprises e.g. (i) transferring dewatered sludge into a pre-treatment unit for temporary storage and odor removal, and (ii) conveying the pre-disposed sludge into a hydrothermal unit, mixing and homogenizing in a homogenizing device, conveying the homogenized sludge into a pulping device, pre-heating and pulping, agitating and pre-heating, conveying the pulped sludge into a hydrothermal reactor, performing hydrothermal reaction, avoiding partial over-heating to prevent coking and carbonizing, and depressurizing to normal pressure.    USE - The method is useful for sludge treatment.    ADVANTAGE - The method ensures good treatment effect, good volume reduction effect, high harmless degree, and good methane recycling and utilizing economic benefits.    DETAILED DESCRIPTION - Sludge treatment based on hydrothermal modification method comprises (i) mechanically transferring dewatered sludge (moisture content 70-85%) into a pre-treatment unit for temporary storage and odor removal, (ii) conveying the pre-disposed sludge into a hydrothermal unit, uniformly mixing and homogenizing in a homogenizing device, conveying the homogenized sludge into a pulping device, pre-heating and pulping by flash exhaust steam back-mixing, mechanically agitating and simultaneously pre-heating by vapor to increase the pulping efficiency, conveying the pulped sludge into a hydrothermal reactor, performing hydrothermal reaction by direct mixing and heating under reverse vapor flow, which is capable of strengthening a mass transfer and heat transfer process, avoiding partial over-heating to prevent coking and carbonizing, then conveying the sludge into a flash evaporator, depressurizing to normal pressure, and applying the flash exhaust steam to a pulping reactor to increase the utilization rate, (iii) cooling the mud pulp discharged from the flash evaporator to 35-45 degrees C using a cooler, and then conveying to a high-pressure diaphragm press filter for filter pressing and dewatering to obtain dewatered mud cakes (solid content 35-45%) and a dewatered filtrate, using the dewatered mud cakes to prepare biomass fuel rods, introducing into a boiler to supply vapor to the hydrothermal unit to perform amount reduction and resource recycling, returning a little of the dewatered filtrate to a hydrothermal system, and conveying the remaining dewatered filtrate into a water treatment system, (iv) conveying the dewatered filtrate firstly into a mesothermal anaerobic reactor and keeping the filtrate in the mesothermal anaerobic reactor for 5.5-7.5 days, controlling the water inflow temperature to less than 40 degrees C, and controlling the anaerobic reaction temperature at 30-40 degrees C, where most of the solid organic substances in the sludge are hydrolyzed and dissolved after mesothermal anaerobic treatment, which rapidly accumulates volatile fatty acids (VFA), greatly improves anaerobic digestion performance, increases methane output and rate, and ensures good recycling value and economic value, and then introducing into a biogas purification unit to prepare compressed natural gas (CNG), and conveying wastewater disposed by an anaerobic reactor into a wastewater treatment plant for treatment, and (v) using the dewatered mud cakes to prepare biomass fuel rods after the mesothermal anaerobic treatment, introducing into the biomass boiler to supply vapor to the hydrothermal reactor and the flash evaporator, and supplementing the biogas produced by parts of the anaerobic digestion sleeve as heat energy.