Abstract: Experiments of tetrahydronaphthalene cracking over Y and ZSM-5 zeolite catalysts under certain reaction temperature and catalyst/oil (C/O) ratio were conducted on a fixed fluidized bed (FFB) unit in laboratory. Test results show that the products of tetrahydronaphthalene cracking over these two zeolite catalysts by naphthenic ring opening reactions were non-aromatics (propane, propylene, butane, butylenes, methylpenptane, cyclopentane, cyclohexane) and monocyclic aromatics (benzene, C1～C4 alkyl benzene). Products of which by dehydrogenation condensation reactions were polycyclic aromatics (naphthalene, alkyl naphthalene, phenanthrenes, pyrenes and so on) and coke. Among them, the relative ratio of naphthenic ring opening reactions to dehydrogenation condensation reactions over Y and ZSM-5 zeolite catalysts was 1.22 and 0.95, respectively. Due to the diffusion and adsorption of naphthenic aromatics on catalysts, the selectivity of naphthenic ring opening reactions are higher over Y zeolite catalyst than those over ZSM-5 zeolite catalyst. Under the conditions of a WHSV of 10 h-1, reaction temperature in the range of 450-550℃, C/O mass ratio in the range of 3-9, the reactions of bimolecular hydrogen transfer and dehydrogenation condensation enhance with the increase of reaction temperature and/or C/O ratio, as a result, the selectivity to the products from naphthenic ring opening reactions decreases.