The invention relates to the pH-sensitive polyurethane and a preparation method and application thereof. The pH-sensitive polyurethane has a structure as shown in a formula I, wherein R is one of materials, m = 2-4, n1 = 20-90, n2 = 20-90, x1 = 1*10< 4>-1*10 < 6 >, and x2 = 1 * 10 < 4 >-1 * 10 < 6 >. The preparation method comprises the following steps of reacting the N, N '-dihydroxyethylpiperazine with the diisocyanate under the action of a catalyst to obtain a double-end isocyanate polyurethane prepolymer, then adding the monoene propyl group polyethylene glycol to react continuously to obtain the pH-sensitive polyurethane, wherein a main chain of a drug carrier obtained by the preparing the polyurethane contains a plurality of pH value sensitive groups, along with the change of the pHvalue of the medium, the expansion degree of the plurality of pH value sensitive groups shows the high pH sensitivity, the mutation range plurality of pH value sensitive groups is less than 0.3 pH value, and the plurality of pH value sensitive groups can be adjusted. Meanwhile, the hydrogel is relatively higher in strength and relatively longer in drug sustained release time, and the drug sustained release time can reach 1-3 weeks.