The invention relates to the field of organic chemical synthesis and discloses a preparation method of alpha-(4-substituted phenyl)isobutyric acid. The method comprises the steps of respectively carrying out Friedel-Crafts acylation, condensation reaction, rearrangement reaction and hydrolytic acidification reaction on single substituted benzene and 2-haloisobutyryl halide or isobutyryl halide serving as an acylating agent to finally prepare a finished product of alpha-(4-substituted phenyl)isobutyric acid. The preparation method provided by the invention has the advantages that the raw materials are easily obtained and are relatively low in toxicity, a catalysis system of the rearrangement reaction can effectively promote the rearrangement reaction, the obtained product is relatively high in purity and yield, the whole preparation method is simple, the adopted reagent is safe, and the preparation method is beneficial to industrial production.