Abstract: Hydrothermal pretreatment and medium-temperature anaerobic digestion improvement method were adopted to improve the methanogenesis of the livestock waste under anaerobic conditions. The effect of the hydrothermal pretreatment on the anaerobic digestion of the cow manure was investigated, and the enhancement mechanisms were explored through the changes in the chemical composition, the elemental composition and the chemical structure of the cow manure after pretreatment. The results showed that a certain intensity of hydrothermal pretreatment could increase the anaerobic methane production of the cow manure, while excessive pretreatment intensity inhibited the methane production. The maximum increase in methane production (176.36 mL) for 4320 min at 70℃ (R₀=3.27) was 21.00% greater than the control group (145.76 mL/g). Under these conditions, the concentration of the acetic acid increased by 65.69%, and the removal rate of the lignin reached 11.50%. The degradation of the organic components and the removal of the lignin were the main reasons for the increase in anaerobic methane yield from cow manure. The elemental analysis indicated that the O/C (w(O)/w(C)) of the cow manure increased after the pretreatment, indicating an increase of the carbohydrate compounds. At the same time, infrared results showed that the extensive R₀ increased the CC bond of the aromatic ring skeleton in the lignin and the lignin-like substances also increased, which leads to a reduction in methane yield. Thus, hydrothermal pretreatment can effectively enhance the degradation efficiency, therefore improving the methane production performance of the substrate.