Abstract: The liquid ion exchange method was employed to prepare cerium (Ce) cation modified Y zeolite (CeY) with various amount of cerium using different types of Y zeolite (HY, USY and NaY) and characterized by X-ray fluorescence spectrometry (XRF), intelligent gravimetric analyzer (IGA) and a molecular simulation technology (Grand Canonical Monte Carlo simulation, GCMC). A novel calculation method of desorption index (DI) has also been proposed to study the influence of cerium cations on the processes of adsorption-desorption of hydrocarbon molecule (benzene) on the CeY zeolites. The saturated adsorption capacity of benzene, adsorption interaction, desorption thermodynamic parameters, potential distribution curves and diffusion processes of benzene in CeY zeolites were analyzed. The results indicate that Ce ion can reduce the desorption activation energy, weaken the adsorption interaction force between benzene and Y zeolites, and modulate the adsorbed state of benzene molecules from agglomerate state to dispersed state, which are main factors to optimize the product selectivity of light oil components in the fluid catalytic cracking (FCC) process with CeY zeolite catalyst.