The diffusion of C4—C24 alkanes, aromatics and cycloalkanes in FAU and MFI zeolites were studied systematically by molecular simulation. The basic data on diffusion energy barriers and the diffusion characteristics of alkanes, cycloalkanes and aromatics in FAU and MFI zeolites were obtained. It was found out that the 12-member-ring openings between the two adjacent super cages limited the diffusion of hydrocarbons in FAU zeolites, and the hydrocarbon molecules diffused more easily in the intersections of MFI zeolite channels than in the straight channels between the intersections. It was more difficult for the molecules to diffuse in the sinusoidal channel of the MFI zeolite than in the straight channel because of the atoms at the corner of sinusoidal channel. The diffusion of three kinds of C6 alkanes was studied by gravity sorption method. The simulation results were well consistent with the experimental results, indicating that the simulation results were convincing. The diffusion of C4-C24 alkanes, aromatics and cycloalkanes in FAU and MFI zeolites were studied systematically by molecular simulation. The basic data on diffusion energy barriers and the diffusion characteristics of alkanes, cycloalkanes and aromatics in FAU and MFI zeolites were obtained. It was found out that the 12-member-ring openings between the two adjacent super cages limited the diffusion of hydrocarbons in FAU zeolites, and the hydrocarbon molecules diffused more easily in the intersections of MFI zeolite channels than in the straight channels between the intersections. It was more difficult for the molecules to diffuse in the sinusoidal channel of the MFI zeolite than in the straight channel because of the atoms at the corner of sinusoidal channel. The diffusion of three kinds of C6 alkanes was studied by gravity sorption method. well consistent with the experimental results, indicating that the simulation results were convincing.