The invention discloses a preparation method for superhydrophobic superoleophilic straw fiber, belonging to the technical field of functional materials. The objective of the invention is to provide the preparation method for the superhydrophobic superoleophilic straw fiber which has cheap and easily-available raw materials, high oleophilic property and biodegradability. The method in the invention comprises the following steps: step 1, crushing straw, soaking the crushed straw in an alkali solution and carrying out pretreatment, and carrying out washing and drying; step 2, with tetraethyl orthosilicate as a silicon source, ammonia water as a catalyst and absolute ethyl alcohol as a solvent, carrying out in-situ synthesis so as to obtain straw fiber with surface loaded with silicon dioxide particles; step 3, dissolving zinc nitrate in a sodium hydroxide aqueous solution, and carrying out vigorous stirring, centrifugal separation and drying so as to obtain zinc oxide particles; step 4, preparing octyltriethoxysilane modified liquid; and step 5, taking the straw fiber in the step 2 and zinc oxide in the step 3, adding the straw fiber and the zinc oxide into the above-mentioned modified liquid, carrying out uniform mixing and dispersing, carrying out filtering separation so as to obtain the straw, and carrying out drying. The superhydrophobic superoleophilic straw fiber prepared by the method in the invention has excellent superoleophilic property and wide application space in the field of marine spilled oil cleaning.