Abstract: The FCC catalysts from Huaxing, Maoming, Jinan Co.were pretreated in 100% steam at the range of 791~800 oC in every 3 ℃ interval for 17 h. The physic-chemical features of aged catalysts were characterized by XRD, N2-adsorption. The catalytic cracking performance of the samples was investigated on MAT and fixed fluidized bed reactor (ACE-MODEL R+ MM). The results show that the structure of molecular sieve in the catalyst aged at 791 oC is kept well and very similar to that of its fresh catalyst, and the crystallinity of molecular sieve is decreased significantly with increasing the aging temperature. The physic-chemical properties and cracking conversion of Huaxing catalyst aged at 797 oC iss equivalent to its equilibrium catalyst. However, the ACE results indicate that yields of carbon deposition, dry gas and LPG are significantly lower than that of its balance agent, and yield of gasoline is opposite. The significant differences in crystallinity compared with equilibrium catalysts exist between the catalysts steam aged at 800℃ from different company. The results show that a relative small change of aged temperature in the range of 791 oC~800 oC can significantly influence on the structure and catalytic cracking activity of aged catalysts. In order to reach the activity the same as the equilibrium catalyst, careful selection and control of the aging temperature based on the properties of fresh catalyst and its application are necessary.