The invention relates to the field of pyrazolo-triazole color formers and particularly relates to a method for preparing 3-dodecylsulfurylpropyl-6-tert-butyl-7H-[1,2,4]-triazol[3, 4-b]-[1,3,4]-thiadiazine. According to the method, the target compound is obtained through converting 4-dodecylsulfurylbutyric acid, which serves as a raw material, into 4-dodecylsulfurylbutyryl chloride in a manner of taking thionyl chloride as a chlorating agent, and then, carrying out dehydration and ring closing with 5-tert-butyl-2-hydrazino-6H-1,3,4-thiadiazine hydrochloride. Compared with the traditional pyrazolone color formers, the compound has the advantages of high coupling activity, low harmful absorption and good light, thermal and wet resistance. A dehydrating agent, i.e., phosphorus oxychloride is not used during synthesis, and thionyl chloride can be recovered, so that environmental pollution is greatly improved, and the method can be applied to industrial production.