The invention discloses a method for preparing 4,4'-biphenol by promoting parachlorophenol coupling reaction by virtue of metal samarium under the catalysis of cupric salt. The method comprises the following steps: mixing parachlorophenol in ionic liquid [bmim]Cl chlorobutyl methylimidazole while stirring for dissolving, and sequentially adding metal samarium powder, anhydrous copper chloride powder; carrying out a reaction system under an anhydrous condition; stirring at the room temperature until the reaction is complete; recycling ionic liquid from obtained reaction mixed liquid; and carrying out column chromatography separation on a crude product, so as to obtain 4,4'-biphenol, and carrying out recrystallization, so as to obtain a pure product, wherein the yield of the pure product is70%-95%.