Abstract: The ultrastable zeolite Y fluid catalytic cracking catalyst was modified by MgO for changing the matrix structure to improve the performance of sulfur transfer. The effect of different conditions and introduction of cerium, lanthanum, phosphor on sulfur transfer was investigated. The result showed that the out-layer Mg-Al spinel was formed on the matrix by modification to bring the catalyst the activity of sulfur transfer. The sulfur transfer activity wasn't efficiently improved by introduction of phosphor but by introduction of cerium and lanthanum. As the reaction temperature raised, SO_2 oxidation greatly (increased.) When there is no oxygen existed, the sulfur transfer activity is very low.