The invention relates to a method for preparing an oil soluble drug sustained release capsule, belonging to the technical field of pharmaceutical preparations. The method comprises the following steps: heating paraffin to a melting state, and then mixing paraffin and oil soluble drug solution to form mixed oily solution; mixing silicon dioxide hydrosol and a surfactant, and stirring and reacting for a period of time to form a mixed aqueous solution; heating the mixed aqueous solution to the highest value of a dissolving process of paraffin, stirring and dropwise adding the mixed oily solution at the same time when the temperature is constant, and then cooling the mixed solution to room temperature; mixing the silicon dioxide hydrosol and the surfactant to form a mixed solution, and adding the mixed solution obtained in the step 3 into the mixed solution and stirring; after reaction is finished, separating, washing by using deionized water and naturally airing to obtain a dried powdery substance; and collecting the powder to obtain the mono-dispersed oil soluble drug sustained release capsule. The method provided by the invention is low in production cost, and the prepared oil soluble drug sustained release capsule has the advantages of controlling release process, reducing the toxic and side effects and reducing drug concentration.