Catalytic cracking assistant capable of increasing concentration of low-carbon olefin and preparation method for catalytic cracking assistant

The invention discloses a catalytic cracking assistant capable of increasing the concentration of low-carbon olefin and a preparation method for the catalytic cracking assistant. The assistant comprises a boron-modified phosphorus and metal containing beta-molecular sieve, a first binder, a second binder and optional second clay, wherein the boron content, calculated as B2O3, of the boron-modified phosphorus and metal containing beta-molecular sieve is 0.5 to 10 weight percent; the phosphorus content, calculated as P2O5, of the boron-modified phosphorus and metal containing beta-molecular sieve is 0.5 to 10 percent; the metal content, calculated as metal oxides, of the boron-modified phosphorus and metal containing beta-molecular sieve is 0.5 to 10 weight percent; the ratio of the peak area of a resonant signal of which the chemical shift is 40+/-3ppm to the peak area of a resonant signal of which the chemical shift is 54+/-3ppm in a 27(superscript) Al MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance) spectrogram of the phosphorus and metal containing beta-molecular sieve is more than 1. The catalytic cracking assistant is applied to the catalytic cracking of petroleum hydrocarbon, the concentration of isobutylene in liquefied gas can be increased, and the yield of coke can be reduced.