The invention discloses functional edible oil and a preparation method thereof. The functional edible oil comprises the following components in parts by weight: 1-20 parts of conjugated linoleic acid, 5-9 parts of linolenic acid, 0.01-0.1 part of antioxidant, 0.01-0.1 part of pentadecyl phenol, 0.01-0.1 part of vitamin E and 70-94 parts of soybean oil, wherein the pentadecyl phenol is extracted from cashew nut shell oil and comprises 6-8 parts of pentadecyl resorcinol and 2-4 parts of pentadecyl phenol. The content of the conjugated linoleic acid in the edible oil can be increased; the antioxidant, the pentadecyl phenol and the vitamin E can inhibit the generation of the trans-fatty acid when the edible oil is heated, induce the trans-fatty acid to be converted into conjugated linoleic acid, promote the conjugated linoleic acid to generate thermotropic isomerization reaction to be converted into conjugated isomers beneficial to the human body and greatly increase the edible health of the edible oil.