The invention discloses an acidic polymer fracturing fluid and a preparation method thereof, and belongs to the technical field of fracturing fluids for oil and gas field development. The acidic polymer fracturing fluid comprises the following components in percentage by mass: 0.25 to 0.60 percent of a polymer thickening agent, 1.0 to 2.0 percent of an anti-swelling agent, 0.2 to 0.5 percent of a discharge aiding agent, 0.3 to 0.7 percent of a cross-linking agent and the balance of water, wherein the cross-linking agent is a mixture of an acidic polymer delayed cross-linking agent and an acidic polymer cross-linking agent, and the mass ratio of the acidic polymer delayed cross-linking agent and the acidic polymer cross-linking agent is 1:2 to 1:3. The cross-linking time of the acidic polymer fracturing fluid can be adjusted between 30 to 120s, the acidic polymer fracturing fluid is higher in anti-swelling rate and proppant carrying capacity, low in rock core damage rate and high in gel breaking performance, the preparation method is simple and convenient in process, and the requirement of revamp for capacity increasing of oil and gas fields can be met.