Abstract: A series of ultrastable Y zeolites with varies Si/Al mol ratio prepared by different dealumination methods have been investigated. After modification by lanthanum incorporation and aging at 800℃ in 100% steam for 4h, the pore structure and acidic property of dealuminated Y zeolites were characterized by nitrogen adsorption and pyridine-IR methods. The catalytic cracking performances were evaluated with microactivity test (MAT) of fluid catalytic cracking (FCC). It is found that LaFSY samples prepared by using (NH4)2SiF6 as the dealumination reactant combined with hydrothermal treatment have homogeneous framework aluminum distribution, and a performance of high cracking activity and low coke yield in FCC is obtained by controlling the dealumination extent using the dealumination method. The LaOSY sample prepared by using oxalic acid as the dealumination reactant combined with hydrothermal treatment has a large mesopore volume which gives the sample a performance of better liquid yield selectivity for residue catalytic cracking.