The present invention relates to the diol intermediate of citalopram useful for treatment of depression, which is the crystal of free base of 3-hydroxylmethyl-4-[1-(4-fluorophenyl)-1-hydroxyl-4-(dimethylamino)]butyl- benzonitrile and the method of crystallization thereof. The present invention has disclosed the method to prepare pure citalopram and its purified salts through crystallization of the described base; the optical resolution method of citalopram diol intermediate, the method to prepare S-citalopram and its purified salts by crystals mentioned above. The present invention has also disclosed the method to prepare citalopram and its purified salts, S-citalopram and its purified salts, as well as pharmaceutical formulation thereof obtained. Using methods of the present invention, the quality and yield of the product can be significantly improved, and the production cost of the medicinal material can be reduced.