The invention discloses an alogliptin benzoate oral solution and a preparation method thereof. The oral solution is prepared from algoliptin benzoate and pharmaceutical adjuvant; and the pharmaceutical adjuvant is prepared from a pH adjusting agent, a flavoring agent, a bacteriostatic agent and water. The preparation method of the oral solution comprises the following steps: (1) adding other components except for the pH adjusting agent into purified water of 80 percent of prescription volume, and stirring and dissolving; (2) adding the pH adjusting agent into a solution of step (1), and enabling the pH value to be 3.0 to 5.0; and (3) supplementing the purified water to the prescription volume, keeping the pH value of the solution at 3.0 to 5.0, filtering by utilizing a 0.8 micro-meter filter membrane, thus obtaining the oral solution. A great amount of experiments finally discover that the alogliptin benzoate oral solution in a given range of pH value has relatively good stability, sothat the problem of the poor compliance of the existing alogliptin benzoate tablet can be improved, and a more convenient drug administration way can be provided for a type-II diabetes patient with the swallowing dysfunction.