The surface acid property of gamma-Al2O3 has been modified by a zeolite Y structure-directing agent (SDA). Thus, modified gamma-Al2O3 as a matrix material was used in fluid catalytic cracking (FCC) catalysts, and its performance of cracking vacuum gas oil (VGO) was evaluated. In comparsion with unmodified gamma-Al2O3, the modified matrix material exhibited superior catalytic performance with heavy oil conversion increased by 5.64%, enhancing the gasoline yield by 2.19% and the LPG yield by 3.00%. Characterization results indicated that the zeolite Y SDA modification effectively introduced Si species into the framework of gamma-Al2O3. The interaction between hydroxyl groups on silanol and Al-OH led to the formation of bridged hydroxyl groups (Si-OH-Al), which are the origin of medium-strength Bronsted acid sites on the modified alumina matrix accounting for the enhanced catalytic performance of FCC catalysts.