Abstract: In order to explore the physicochemical characteristics and organic matter migration characteristics of thermal hydrolysis pretreatment on high solids sludge, a small thermal hydrolysis reactor was used to simulate the sludge hydrolysis test indoors, and the viscosity of thermal hydrolysis treatment on high solids sludge. Specific resistance, thermal conductivity and other physical characteristics and the influence of organic matter migration characteristics such as COD dissolution rate, SS dissolution rate and VSS dissolution rate was studied. Results show that after thermal hydrolysis treatment of urban sludge with solids content of 9% at 190 ℃ and 50 min, the thermal conductivity was increased by about 15%, and the viscosity and specific resistance were reduced by about 99.5%. The COD dissolution rate, SS dissolution rate, and VSS dissolution rate of the sludge were about 40%, 35%, and 70% under the conditions of 170 ℃ and 30 min thermal hydrolysis treatment, respectively. Thermal hydrolysis treatment can improve the physical properties of sludge for facilitating subsequent treatment; the COD in the sludge was also transferred from the solid phase to the liquid phase, which improved the anaerobic digestion performance of the sludge. During the thermal hydrolysis of the sludge, the kinetic model of the organic matter showed that the dissolution of the VSS in the thermal hydrolysis process was in line with the first-order reaction kinetic model by R²=0.990 9, P < 0.01.