The invention discloses a method for preparing a rosuvastatin midbody. The method comprises the steps of weighing lewis acid MgCl<2>, aromatic aldehyde, isobutyryl acetate and thiourea, wherein the mole ratio of aromatic aldehyde to isobutyryl acetate to thiourea is 1:1-1.5:1-2.0, and the mole number of a lewis acid catalyst accounts for 5-20% of the total mole number of aromatic aldehyde, isobutyryl acetate and thiourea; adding aromatic aldehyde, isobutyryl acetate, thiourea and the lewis acid catalyst MgCl<2> into a reaction vessel, adopting 1, 4-dioxane as solvent, stirring the mixture and raising the temperature, after the reaction is conducted sufficiently, getting a reaction solution to be subjected to cooling, washing, extraction, drying, filtration and reduced pressure distillation, then conducting column chromatography isolation, and obtaining the rosuvastatin midbody, namely 4-(4-fluoro-phenyl)-6-isopropyl-2-thiocarbonyl-1, 4-dihydropyrimidine-5-acetate. By means of the method, the rosuvastatin midbody high in purity can be obtained, the catalyst is low in price and easy to obtain, reutilization can be conducted, and the production cost is lowered.