The invention discloses a catalytic cracking auxiliary agent containing a phosphorus-containing and supported-metal-containing Beta molecular sieve, and a preparation method thereof, wherein the catalytic cracking auxiliary agent contains 10-75 wt% of a phosphorus-containing and supported-metal-containing Beta molecular sieve (calculated as the dry base), 3-30 wt% of a phosphorus-aluminum inorganic binder containing first clay (calculated as the sum of the dry bases of Al2O3, P2O5 and the first clay), 3-30 wt% of other inorganic binders (calculated as the oxide), 0-60 wt% of second clay (calculated as the dry base), and 0-15 wt% of a group VIII metal additive (calculated as the oxide) by using the dry base weight of the auxiliary agent as the reference. According to the present invention,with the application of the catalytic cracking auxiliary agent in the catalytic cracking, the yields of isobutylene and propylene can be improved, and the octane number of gasoline can be increased.