Abstract: In order to reveal the depolymerization mechanism of α-O-4 linkages in lignin during the process of py-rolysis，phenolglycerol-α-phenyl ether is selected as the α-O-4 lignin dimer mold compound，and its pyrolysis behaviors at 773K and 101kPa are simulated according to the density functional theory (DFT)． Then，the enthalpy changes of each step are calculated． It is found that the dimer pyrolysis starts from the dissociations of C_α —O and C_α —C_β bonds． According to the thermodynamics possibility，the following pyrolysis is designed into differentpaths，and the final pyrolytic products are found to contain small molecule compounds (methanol，ethanol，ethylene glycol and ethylene oxide)，phenol and para-substituted phenols (p-methyl phenol，p-ethyl phenol and p-hydroxybenzyl alcohol)，benzene and substituted benzene (benzyl alcohol)． In all these phenolic compounds，p-methyl phenol and p-ethyl phenol are the most possible products，which are followed by phenol． In addition，the pyrolysis behaviors of α-O-4 and β-O-4 lignin dimers are compared． The results show that all the differences between the two lignin dimers are attributed to their different structures．

Key words: lignin dimer, pyrolysis, density functional theory, α-O-4 linkage