Abstract: A series of porous silica-alumina materials with different pore structure and acidity was prepared through co-gel，aging and post-treatment process，the structural properties was characterized by XRD，BET，FT-IR，NH3-TPD，and the cracking activities of the catalysts preparated by these materials were evaluated with the heavy oil micro-reactor. The results revealed that the materials with pore diameters of 7-14 nm，total acid contents of 0.617-1.046 mmol/g，and with both Br?nsted acid and Lewis acid are obtained by the adjustment of preparation conditions. Pore structure and acidic property as well as hydrothermal stability play important roles on cracking activity and product distribution，but pore size and acidity have different effects. When the pore size is between 11-14 nm after hydrothermal ageing treatment，the functions of pore structure and acidic property are complementary and promote the activity of cracking. As the pore sizes become larger，the effect of pore structure on cracking is much stronger than that of acidity. For acidity，the cracking activity is affected dramatically by the total acid content，but the product distribution mainly depends on the distribution of acid centers.

Key words: silica-alumina material, pore structure, acid content, acid center distribution, FCC