The invention provides a method for synthesizing (E)-alpha, beta-unsaturated carbonyl compound by adopting reaction control and self-separation technology. The method takes ionic liquid as solvent, aldehyde and ketone as materials, bridge sulfur atom ligand-containing organic bismuth ion complex as main catalyst and fatty amine as auxiliary catalyst for reaction. The synthesis method opens up a new environment-friendly approach for preparing (E)-alpha, beta-unsaturated carbonyl compound with low cost, and has the advantages that both the selectivity and the yield of the target product are nearly 100%; the reaction is homogeneous reaction and products are separated to two phases automatically after the reaction; the catalysts can be directly recycled in the ionic liquid; pure (E)-alpha, beta-unsaturated carbonyl compound can be obtained by separating the products simply through distillation under reduced pressure; and no normal organic solvents are necessary in the whole reaction and separation process, so the method is environment-friendly.