The invention discloses a refining method of a key intermediate of 2-(1-benzyl-piperidine-4-methyl alkenyl)-5, 6 dimethoxy-indanone of Donepezil, namely, a compound (I), and the method is to obtain the high purity compound (I) by agitating a crude product of the compound (I) in the presence of inorganic base in a benzenoid aromatic hydrocarbon-containing organic solvent of C6 to C12 at a certain temperature. The method has advantages of simple operation, short reaction time, single solvent and low cost, and is suitable for the industrialized production.