Fluid catalytic cracking (FCC) has been the most important and flexible conversion process in petroleum refineries. It is economically beneficial in allowing low-value materials of high molecular weight to be cracked into valuable constituents, such as gasoline, diesel and petrochemicals. Therefore, understanding the reaction mechanism of heavy molecules is a key to increase the selectivity of valuable products. To improve FCC performance, generalization of the main factors affecting catalyst structures, feed properties and operation conditions is crucial. Our work mainly focuses on the metal deactivation behavior of residual fluid catalytic cracking (RFCC) catalysts. Catalyst cracking activity relates amount of metal on the catalyst. If two kinds of deactivation, steam and metal poisoning, are considered, the catalytic property of the equilibrium catalyst in a RFCC unit can be expressed. It can be used, for example, as the RFCC catalyst deactivation reduction ratio in analyses of the influence of the regenerator condition of RFCC unit according to this model. As a result, a circulating fluidized bed reaction system model for estimation of FCC catalyst activity was developed and used to evaluate the effects of regenerator condition on catalyst deactivation.