Abstract: In this paper, the reaction mechanism concerning hydrothermal liquefaction of biomass is introduced, as well as the recent research progress in this area worldwide. Based on elaborating the reaction mechanism of monomers, such as monosaccharides, glucose, xylose and amino acids, the reaction mechanism of polymers including lignin, cellulose and protein etc. was analyzed. Finally, the liquefaction mechanism of lipid and its derivatives under hydrothermal condition is reviewed as well.

Key words: biomass, hydrothermal liquefaction, bio-oil, mechanism