The invention discloses a method for separating 4-acetoxy-2-methylene-butyraldehyde from a hydrogenated product, i.e., 4-acetoxy-2-methyl-butyraldehyde thereof. The method comprises the steps of (A) putting a mixture of the 4-acetoxy-2-methylene-butyraldehyde and the 4-acetoxy-2-methyl-butyraldehyde into a reactor together with dienophile so as to enable the 4-acetoxy-2-methylene-butyraldehyde to have a Diels-Alder reaction with the dienophile, wherein the 4-acetoxy-2-methyl-butyraldehyde does not react; (B) separating the 4-acetoxy-2-methyl-butyraldehyde from a condensation product of the Diels-Alder reaction to obtain the 4-acetoxy-2-methyl-butyraldehyde product; (C) carrying out thermal cracking on the condensation product of the Diels-Alder reaction under the condition that ionic liquid is taken as a solvent so as to obtain the 4-acetoxy-2-methylene-butyraldehyde and the dienophile; after that, separating the 4-acetoxy-2-methylene-butyraldehyde from the dienophile (such as by rectifying) to obtain the 4-acetoxy-2-methylene-butyraldehyde.