Cracking aid for improving lower-carbon olefin concentration

The inventive cracking aid for improving lower-carbon olefin concentration comprises a phosphorus/aluminum inorganic binder containing a first clay, a modified MFI molecular sieve, other inorganic binder, group-VIII metal additive, and optional a second clay. The first inorganic binder comprises aluminum component (as alumina) 15-40 wt%, phosphorus component (as phosphorus pentoxide) 45-80 wt%, and the first clay (on dry basis) 1-40 wt%. The cracking aid is used for catalytic cracking of petroleum hydrocarbons, can increase yield of catalytic cracked liquefied gas and obviously improve lower-carbon olefin (especially propylene) concentration in liquefied gas, and has high heavy oil conversion ability.