The invention discloses a preparation method of 3-methyl-2-butena. According to the preparation method, in the presence of an acid catalyst, a vanadium-manganese-iron composed composite catalyst is adopted for catalysis, raw material 2-methyl-3-butine-2-ol catalytic rearrangement is carried out to prepare 3-methyl-2-butena; wherein in the composite catalyst, vanadium is vanadic anhydride, manganese is manganese dioxide, and iron is ferriferrous oxide or iron oxide. The preparation method is capable of increasing 3-methyl-2-butena conversion rate greatly, and reducing the yield of dehydroxylation by-product after reaction; in the reaction process, a synthesis reaction vessel is taken as a reaction container, full mixing of the catalyst with reaction raw materials is realized, adhesion of the catalyst on vessel wall or involving into formed whirlpool is avoided, and the using effect of solid state catalyst is improved.