In order to improve the product quality and yield by finding out the optimal technol. conditions, thiotriazinone sodium was synthesized by condensation of 2-methyl-3-thiosemicarbazide, di-Et oxalate and sodium methoxide in a mixed solvent (a polar proton solvent and a polar non-proton solvent) at 0∼45°C, and then the target product thiotriazinone (TTZ) was obtained by hydrochloric acid acidification.By using mixed solvents, the viscosity of the synthesized process system was greatly improved, the yield of thiotriazinone (TTZ) was increased to more than 90% (calculated by 2-methyl-3-thiosemicarbazide), and the average purity was over 99.5%, the byproduct material, 1-methyl-5-mercapto-1,2,4-triazole-3-carboxylate (TTA), was less than 0.1%.So, this industrial method is suitable for the synthesis of thiotriazinone (TTZ).