NOVELTY - An escitalopram oxalate preparing method involves dissolving D-bi-paramethyl benzol formyl tartaric acid salt of S-diol in water. Sodium hydroxide solution is utilized for neutralizing the dissolved salt to obtain free S-diol. Cyclization reaction is carried out after adding paratoluensulfonyl chloride reaction product is blended for 2.0-4.0 hours to separate reacted liquid. Oxalic acid is added, and the reaction product is blended for 1.5-2.5 hours to generate salt. The temperature is reduced to minus 5-5 degrees C, and the salt is filtered and dried at 50 plus minus 5 degrees C to obtain escitalopram oxalate.    USE - Method for preparing escitalopram oxalate.    ADVANTAGE - The method enables performing cyclization reaction by utilizing water as solvent under mild condition in an environment-friendly manner. The method enables preparing escitalopram oxalate, thsu achieving high yield. The reaction product can be easily separated and purified. The raw materials can be easily obtained, and the preparation operation can be progressed in a simple manner, thus ensuring easy industrial production.    DETAILED DESCRIPTION - An escitalopram oxalate preparing method involves dissolving D-bi-paramethyl benzol formyl tartaric acid salt of S-diol in water. Sodium hydroxide solution is utilized for neutralizing the dissolved salt to obtain free S-diol. Temperature is controlled at 0-10 degrees C, and paratoluensulfonyl chloride is added. 1.5-2.5 mole/L of inorganic alkali solution is added, and cyclization reaction is carried out for 0.5-1hours. The reaction temperature is controlled at 0-10 degrees C, and the reaction product is blended for 2.0-4.0 hours, where mol ratio of the paratoluensulfonyl chloride, the inorganic alkali in the inorganic alkali solution and the raw material, D-biparamethyl benzol formyl tartaric acid salt is 1.05-1.5: 1.2-1.6: 1. The sodium hydroxide solution is again added after ending up the reaction. Power of Hydrogen value is adjusted to 12-13. Water phase is extracted for three times by utilizing organic solvent, and organic phase is merged. The reaction product is washed by the water, for one time to separate reacted liquid. Oxalic acid is added to the obtained liquid, where the mol ratio of the oxalic acid and the raw material, D-bi-paramethyl benzol formyl tartaric acid salt is 1.05-1.3: 1. The reaction temperature is controlled at 20 plus minus 10 degrees C, and the reaction product is blended for 1.5-2.5 hours to generate salt. The temperature is reduced to minus 5-5 degrees C, and the salt is filtered and dried at 50 plus minus 5 degrees C to obtain escitalopram oxalate.