The invention discloses a method for synthesizing a herbicide raw medicine, and relates to the pesticide production field. The method includes six technological processes of raw material preparation, reaction kettle mixing preheating, solution neutralizing treatment, sulfonation reaction, amination reaction and washing layering treatment; with use of the sulfonation reaction of 2,6-dinitro p-tert chlorobenzene and sodium pyrosulfite and the amination reaction of 2,6-dinitro p-tert chlorobenzene and sec-butylamine, the herbicide raw medicine with relatively high purity can be prepared; moreover, with multiple use of clear water for washing, the production process is simple and reliable, recrystallization is not needed, the high-purity product can be obtained, the yield and the product purity are high, an efficient herbicide product can be obtained, and the method is worthy of promotion.