Catalytic pyrolysis of heavy oils on various catalysts was investigated in a confined fluidized bed reactor. As for catalytic pyrolysis of Chinese Daqing atmospheric residue (Daqing AR) on catalyst CEP-1, reaction temperature, residence time, weight ratios of catalyst-to-oil, steam-to-oil and feed properties have significant influence on product yields and product distribution. The optimal laboratory operating conditions are as follows: reaction temperature is within 650-680 degrees C, residence time within 2.0-4.0 s and catalyst-to-oil weight ratio within 13-18. The catalytic pyrolysis ability becomes better and the yields of light olefins become higher with the larger HIC moll ratio and the lower aromatic carbon content of feedstocks. After the cracking mechanisms of hydrocarbons are analyzed and the thermal pyrolysis of Daqing AR is investigated, a mechanism Parameter R-M is proposed to Study the mechanistic pathways of heavy oil catalytic pyrolysis. As for the processes of Daqing AR catalytic pyrolysis on catalysts LCM-5 and CEP-1, the relative acting percentage of the free radical mechanism and that of the carbonium ion mechanism are obtained. (c) 2005 Elsevier B.V. All rights reserved.