Abstract: Structure oriented lumping was applied to construct a catalytic cracking kinetic model of vacuum gas oil (VGO) on molecular level. 686 kinds of single-core molecules were selected to form a matrix of VGO feedstock and non-linear least squares method was used to obtain the percentage of individual molecule. 60 reaction rules were proposed to build a complex reaction network including more than 40 000 times of reactions. To reduce the number of variable parameters, rate constants were calculated by 5 segments. The reaction network was solved by matrix transformation instead of Runge-Kutta method and product distributions could be obtained. Experimental data were collected from catalytic cracking of mixed Middle East VGO performed on a XTL-6 type of riser reactor for model verification. Comparison results showed that the calculated values of product distributions agreed well with the experimental data, the relative errors were less than 10%. Besides, this model exhibited well adaptability with the changing of reaction temperature and catalyst to oil ratio.