Abstract: In order to better understand the slurry-bed hydrocracking of medium and low temperature coal tar,a series of experiments were conducted in an autoclave. The composition changes of coal tar before and after hydrocracking were characterized by distillation,SARA fractions,and elemental analysis. The properties of asphaltenes such as structure parameters and functional group were analyzed by FT-IR and 1H-NMR. The results show that the coal tar has a low coking yield in the hydrocracking process,and the reaction depth could be increased by enhancing the reaction temperature in definite range. The asphaltenes content of hydrogenation products is reduced sharply and the oxygen content of asphaltenes decreases,while the average molecular weight,the aromatic-carbon ratio and condensation degree of asphaltenes increase. It has been seen that the cyclization reactions and removal of alkyl side chins and oxygen (especially the oxygen of phenolic hydroxyl and ether group) occur on the asphaltenes during the process of hydrocracking,making most of asphaltenes conversion to light fraction.