Abstract: The USY FCC catalyst was modified by MgO for changing the matrix structure to improve the performance of sulfur transfer and was modified by Ce2O3, La2O3 and P2O5 for enhancing the activity of sulfur transfer. The properties of modified catalyst were investigated by FTIR. The effect of MgO, Ce2O3, La2O3 and P2O5 on the activity of sulfur transfer and catalytic cracking reaction were investigated. The result show that the modified catalyst keeps up good activity of sulfur transfer which is kept more than 6% after many times of oxidationreduction cycle. The introduction of a few MgO decreases the amount of stronger acid on the surface of matrix and zeolite, but does not greatly influence the activity of catalytic cracking reaction. The introduction of rare earth metal increases acid amount of the matrix and zeolite, and promotes catalytic cracking reaction. But high content of rare earth metal also promotes formation of coke. The addition of 1% P2O5 optimizes the acidic properties of the matrix and zeolite to produce the low coke yield. The good activity of catalytic cracking reaction is kept up while the olefin content in catalytic cracking gasoline is reduced 6 percent.