The experiments of Poplar （Populus×euramericana cv.‘I-214’） and Chinese Fir（Cunninghamia lanceolata） wood flour liquefied in the presence of phenol under sulfuric acid catalysis were conducted. The effects of reaction time and reaction temperature on the wood liquefaction were investigated. By means of gel permeation chromatography（GPC） analysis, the molecular weights of liquefied wood under different reaction conditions were measured to trace the change in the structural characteristics of the liquefied wood. The insoluble residues were analyzed by Fourier transform infrared to investigate the liquefaction order of three main wood components. The results showed that 1) the liquefaction curves for the Chinese Fir and Poplar were similar in general. The acidic catalyst showed a function not only on cellulose and hemicellulose, but also on lignin. 2) The reaction temperature had the greater influence on the residue content than reaction time. Both reaction temperature and reaction time could affect the molecular characteristics of liquefied wood. The weight-average molecular weight of liquefied Chinese Fir was higher than that of liquefied Poplar under most of the reaction conditions. 3) During wood liquefaction, lignin and hemicellulose were liquefied first and cellulose being the most difficult to liquefy. The decomposition, phenolation and recondensation of wood components are three main reactions which dominated the whole liquefaction dynamic process and determined the structural characteristics of liquefied wood.