NOVELTY - Synthesis of thiamine disulfide involves: reacting liquid methanol with sodium free acetamidine hydrochloride, adding alpha -(o-chlorophenylaminomethyelne)- beta -formylaminopropionitrile, and cyclization to form ring closed product, adding water and carbon disulfide, reacting at 30-40 degrees C for 1-3 hours, adding gamma-chloro-gamma-acetyl-propanol, carrying out condensation reaction and filtering; dissolving obtained crude product in hydrochloric acid, heating followed by decolorizing, filtering, neutralizing, separating precipitate and drying.    USE - For synthesis of thiamine disulfide (claimed) which is used as intermediate for the synthesis of vitamin B1.    ADVANTAGE - The present process provides simple step; produces thiamine disulfide with high yield; reduces the generation of waste; protects the environment; and reduces production cost.    DETAILED DESCRIPTION - Synthesis of thiamine disulfide involves: a) mixing liquid methanol with sodium free acetamidine hydrochloride, then filtering to obtain filtered liquid, putting the filtered liquid in the reactor, and adding alpha -(o-chlorophenylaminomethyelne)- beta -formylaminopropionitrile, then recovering methanol and cyclization, to obtain ring closed product; b) subjecting the ring closed product to steam distillation at 120 degrees C, and then condensing solution, after completion of the reaction collecting the o-chloroaniline solution from the bottom layer; c) after ending the steam distillation, adding liquid alkali, hydrolysis, then adding water and carbon disulfide and reacting at 30-40 degrees C for 1-3 hours, at last adding gamma-chloro-gamma-acetyl-propanol, subjecting to condensation reaction, then filtering to obtain crude thiamine thiosulfate; d) dissolving the obtained crude product in hydrochloric acid, heating to 70-95 degrees C for 1 hour, followed by addition of 1.6-2 g decolorizing charcoal, decolorizing for 32-35 minutes, filtering, neutralizing the filtered solution to pH 7.2-7.3 until a solid precipitate was formed, separating solid precipitate and then drying to obtain thiamine disulfide.