The invention discloses a cationic polymerization method. The method comprises the step that under the condition of cationic polymerization, at least one kind of monoolefine and at least one kind of alkylstyrene are in contact with each component in an initiator system in at least a diluent, wherein the initiator system contains at least a compound, at least a Lewis acid and at least an activator; the compound can provide carbocations; the activator is selected from a compound shown in a formula I-1 and a compound shown in a formula I-2. When alkylstyrene and monoolefine are copolymerized in the low-polarity diluent through cationic polymerization, the copolymerization activity of alkylstyrene can be obviously improved by adopting the method, thus improving the polymerization efficiency of a polymerization system and achieving higher polymer yields. Besides, polymers with different molecular weights can be prepared under different polymerization conditions by adjusting the composition of the initiator system according to the method so as to meet the requirements of different application occasions. The formula I-1 and the formula I-2 are shown in the specification.