Cracking auxiliary agent for raising density of propylene

The present invention discloses a method for increasing the concentration of propylene in the cracking aid, which on a dry basis weight of from 10 to 65% of the modified ZSM-5 zeolite, 0 to 60 weight% of clay, 15 to 60% by weight of the inorganic oxide binder, one or more of 0.5 to 15 weight percent of a metal selected from a group VIIIB metal additive, and 2 to 25% by weight of a phosphorus additive, wherein said modified ZSM-5 zeolite by and P is selected from Fe, Co or metal-modified one of Ni, its anhydrous chemical formula, in terms of oxide is (0 ~ 0.3) Na 2 O · (0.5 ~ 5) Al 2 O 3 · (1.3 ~ 10) P 2 O 5 · (0.7 ~ 15) M x O y · (70 ~ 97) SiO 2 , x represents the number of atoms of M, y represents a number needed for satisfying the oxidation state of M, and said metal additive is a phosphorus additives are oxides. The additive in the cracking of petroleum hydrocarbon catalytic cracking process, FCC liquefied increase and improve the yield of FCC gasoline octane while, can significantly improve the propylene concentration in the liquefied gas.