Abstract: The effect of partial hydrogen pressure within 3MPa~28MPa on cracking of butylbenzene and tert-butylbenzene were examined in a batch reactor. Pressure has different effects depending on the molecular structure of reactants. With the raising of partial hydrogen pressure, the cracking reaction of tert-butylbenzene is prompted, while the conversion of butylbenzene is restricted. In any case, the break of C—C bonds between the aromatic ring and the whole branch chain are promoted with the increasing of partial hydrogen pressure. Based on the above result, the effect of initial hydrogen pressure on slurry bed hydrocracking of Lungu and Karamay atmospheric residues was studied. With the raising of initial hydrogen pressure, the reactions of hydrocracking and the formation of toluene insoluble fraction are promoted simultaneously. Effects of reaction temperature and time are also discussed.