Three different zeolite catalysts with different pore sizes (MFI-type, BEA-type, and FAU-type zeolites) have been prepared. The influence of different zeolite catalysts on reactivity and product shape selectivity of tetralin is investigated. Clear differences are observed in the reactivity of tetralin and distribution of products achieved by different catalysts. The diffusion and adsorption behavior of the reactant tetralin and its intermediates, n-butylbenzene and 1-methylindane under the reaction conditions are simulated using molecular simulation methods. Upon combining simulation results and experimental observations, it is shown that the difference in diffusion coefficient and competitive adsorption capacity can explain the reactivity of tetralin and the selectivity of products. The steric hindrance of the MFI-type zeolite mainly limits the key step of ring opening of tetralin, leading to lower selectivity of ring-opening products. n-Butylbenzene molecules can diffuse sufficiently fast in the large pores of FAU-type zeolite and the weak adsorption capacity of n-butylbenzene leads to its insufficient cracking. In addition, it also explains the reason that the BEA-type zeolite has the best BTX selectivity, because it can satisfy both good ring-opening activity and sufficient butylbenzene cracking depth.