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 hydrothermal deactivation behavior of residual fluid catalytic cracking (RFCC) catalysts. There are two steps in this deactivation: an initial rapid drop followed by gradual decline in activity. During the first step, collapse of the outside of zeolite micropores was mainly observed. At that time, significant amount of coke was formed and overcracking occurred, as shown by the MAT result. In the following step, the rate of coke formation and overcracking of the gasoline fraction decreased. Subsequently, the gasoline yield decreased, probably because of gradual and even dealumination of the zeolite crystals, resulting in a lower surface area of zeolite. Finally, the catalyst structure stabilized under the hydrothermal conditions.