The invention discloses a method for synthesizing cyhalofop butyl intermediate(R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy] propionic acid.(S)-2-chloropropionic acid methyl ester and p-chlorophenol are used as raw materials, an etherification reaction is performed under an alkaline condition to generate(R)-2-(4-hydroxyphenoxy)propionic acid, and the etherification product and 3-fluoro-4-hydroxybenzonitrile generate the(R)-2-[4-(4-cyano-2-fluorophenoxy)phenoxy] propionic acid under the action of an acid-binding agent. According to the method, the problems of serious excessive hydroquinone servingas a raw material, massive use of an inorganic base and generation of dietherification byproducts in synthesis are avoided. The method is high in atom utilization rate, high in reaction yield and lowin production cost.