Abstract: The behaviors of mild liquefaction of a lower rank coal (HL lignite) were investigated using a tube bomb reactor with respect to the influence of reaction temperature, solvent, initial pressure, atmosphere and catalyst. TPD-FID(temperature programmed decomposition-flame ionization detector)and FT-IR were used to study the properties of liquefaction residues (hexane insoluble part). The gel permeation chromatography, synchronous fluorescence and infrared spectroscopy were used to study the structure characteristics of asphaltenes (A) and preasphaltenes (PA) produced. The results show that the notable liquefaction of HL lignite starts at about 350℃. The increase of liquefaction yield increases with the increase of the temperature. As the condensation reaction becomes significant at the higher temperature (450℃), the liquefaction yield starts to decline. The solvent can significantly improve the yields of A+PA. The increase of reaction pressure and the addition of catalysts mainly lead to an increase of Oil+Gas (O+G) yield. The liquefaction residue (hexane insoluble) obtained under mild conditions has a higher pyrolysis reactivity than its parent coal. When the liquefaction temperature is higher than 300℃(350℃), the molecular weight and the paraffinic characteristics of asphaltene (preasphaltene) decrease with liquefaction temperature.