Modified molecular sieve as well as preparation method and application thereof

The invention relates to a preparation method of a modified molecular sieve. The preparation method comprises the following steps that: a molecular sieve is provided; the molecular sieve is arranged in an acid solution for acid treatment to obtain a prefabricated molecular sieve; and the prefabricated molecular sieve is placed in a modifier solution for modification treatment to obtain a modifiedmolecular sieve, wherein the modifier is halogenated dimethyl benzyl alkylammonium, wherein the halogenated dimethyl benzyl alkylammonium has a structural formula shown in a formula (I) described in the descriptions, according to the formula, R is selected from alkyl, and X is selected from halogen. The invention also relates to a modified molecular sieve and application of the modified molecularsieve. When the modified molecular sieve disclosed by the invention is used as a catalyst for cracking reaction, the reaction selectivity of the modified molecular sieve is high, the generation amountof impurities in a crackin