The invention discloses imidazole salt type cationic polyurethane and a preparation method thereof. The preparation method comprises the following steps: 1) mixing 1mol of dibromoneopentyl glycol with 2mol of imidazole compound to react and obtain imidazole salt glycol; and 2) mixing 1-10mol of imidazole salt glycol, 1-10mol of long-chain glycol with the weight average molecular weight of 100-2000, 1.8-20mol of diisocyanate, tetrahydrofuran and 2-3 drops of catalyst to react in the atmosphere of nitrogen and obtain the cationic polyurethane, wherein the molecular structure of the imidazole salt type cationic polyurethane is AxByCz, A is imidazole salt glycol, B is diisocyanate, C is long-chain glycol; and (x+z)/y=1.0-1.1; and the ratio of x to z is 0.1-10.0. In the preparation method of the invention, the charged functional groups of glycol are expanded, imidazole salt glycol ionic liquid is introduced and the imidazole salt type cationic polyurethane is prepared; and the electrophoretic mobility can not be damaged by acid or base. Cationic polyurethanes with unequal electric charges can be prepared by adjusting the proportion of imidazole salt glycol; and the cationic polyurethane can be coated on elements through electrostatic adsorption, thus better protecting and stabilizing the base material.