Abstract: Kuwait vacuum residue is cut to 4 narrow fractions by SFEF and the residue and all the fractions are characterized by NMR and mass spectrum. The experiments of contact thermal cracking reaction of Kuwait residue and its fractions were conducted over inert particle in a laboratory fixed fluidized reactor. The results show that the yields of dry gas, coke and liquid increase linearly with the content of cores containing five or more aromatic rings, fA and (fN+ fP)，respectively. At the same process condition, the value of CH4/C3H6 as the index of cracking severity of feeds rises linearly with the content of cores containing five or more aromatic rings. The heavier the feed is, the lower the selectivity of hydrogen is, while the methane, ethane, propane and butane have the opposite results. The proportion of the hydrogen distributed in dry gas and coke is higher with the feed becoming heavier and meanwhile the proportion is lower in liquid.