In this paper, the key intermediate of 2-methoxylcarbonyl-5-methylsulfonylaminomethylbenzene sulfonamide (6) was prepared starting from p-tolunitrile via chlorosulfonation-aminiation, oxidation, reduction, methlsulfonylation and alcoholysis. Subsequently, the aimed product of mesosulfuron-methyl (7) was achieved from 6 and 4,6-dimethoxy-2-(phenoxycarbonyl)aminopyrimidine, the total yield of the six-steps was 33.3%. The structures of target product and intermediates were determined by IR, 1H NMR and MS. Compared with the synthesis process in references, this synthetic route is cost-effective, simple operation, high yield and valuable for the industrial application.