Woody biomass was liquefied by water in an autoclave in the reaction temperature range of 280-420℃with sodium carbonate as the catalyst. The experimental results show that the yield of the main liquefaction product (heavy oil) was significantly influenced by the process conditions. The maximum yield of heavy oil was obtained at reaction temperature 380℃. The heavy oils obtained at different reaction temperature were analyzed by Fourier transform infrared spectroscopy (FTIR) and gas chromatography/mass spectrometry (GC/MS). The analytical results show the heavy oil is complex compound that contain hydrocarbon, aldehyde, ketone, hydroxybenzene and ester.