The invention discloses a synthetic method for olefin compounds. According to the synthetic method, a functionalized ionic liquid is taken as a catalyst, and the reactants are catalyzed and subjected to an alkylation reaction for synthesis of the olefin compounds. The catalyst is an acid-functionalized ionic liquid belonging to a nonmetal system and is environment friendly; the catalyst is small in use amount, high in catalytic activity, good in stability and low in corrosivity; the synthetic method has good product selectivity, simple operation, strong controllability, wide substrate application scope, mild reaction condition, simple post treatment and easy separability between the products and the catalyst; and the catalyst is reusable.