The invention discloses a phenyloboricacid-modified cationic polymer, the structural formula is that (see lower right): wherein R is H or alkyl group containing one to ten carbons or substitution alkyl group containing nitrogen, oxygen, sulfur, chlorine, bromine or iodine; P is cationic polymer, the molecular weight Mw of P is from 400 to 500000, and n is more than or equal to 1 and less than or equal to 20. The preparation method is that: the phenyloboricacid with active groups and the cationic polymer are dissolved in methyl alcohol in N, N-dimethyl fomamide, and are reacted for 2-48 hours at the temperature of 20-60 DEG C for obtaining the phenyloboricacid-modified cationic polymer. The cationic polymer utilizes functional groups such as hydroxide radical and amino-group and the like in biomacromolecules such as phenyloboricacid group energy, protein, amylase, nucleic acid and the like to form reversible covalent-binding property, and improves the capacity of gene combination and cell carrying of carrier materials, so as to realize high-efficiency transfection of genes.