Abstract: The present invention relates to a method for purifying key intermediates of Citalopram, i.e. 4-[4-(dimethylamino)-1-(4-fluorophenyl)-1-hydroxybutyl]-3-hydroxymethylbenzonitrile and a salt thereof. The method comprises dissolving crude 4-[4-(dimethylamino)-1-(4-fluorophenyl)-1-hydroxybutyl]-3-hydroxymethylbenzonitrile (compound of formula I containing formaldehyde impurity) with an organic solvent, adding a washing solution, controlling the temperature, stirring, leaving to stand for layering, and removing the aqueous layer, so as to obtain a purified organic solution of 4-[4-(dimethylamino)-1-(4-fluorophenyl)-1-hydroxybutyl]-3-hydroxymethylbenzonitrile. The method provided by the present invention can effectively remove aldehyde group-containing impurities in the intermediate. The method of the present invention has the advantages of simple operation, cheap raw materials and mild conditions, and is suitable for large-scale industrial production.