The invention discloses a synthetic method for a kind of polysubstituted baicalein derivatives shown as a formula I, and in the formula I, R1, R2 and R3 are H, hydroxyl, alkyl, alkoxy and the like. By modifying baicalein B-ring skeleton, the baicalein derivatives are synthesized, which are substantially improved in dissolvability, anticancer activity and other aspects compared with baicalein. The method employs substituted benzaldehyde and 3,4,5-trimethoxyphenol as basic raw materials, and the B-ring polysubstituted baicalein derivatives are prepared through 3 steps. The method concretely comprises performing condensation reaction on the substituted benzaldehyde and an acid anhydride under the effect of an alkali catalyst, so as to obtain substituted cinnamic acid, and further synthesizing substituted cinnamoyl chloride, performing acylation reaction on the substituted cinnamoyl chloride and 3,4,5-trimethoxyphenolunder the effect of a catalyst, so as to obtain a chalcone compound, and performing cyclization reaction on the chalcone compound under the effect of a catalyst, so as to obtain the corresponding polysubstituted baicalein derivative. The method is simple in technology, abundant in raw materials, high in yield, good in product purity and low in cost, and has wide application prospect.