Improved synthetic method of penoxsulam

The invention discloses an improved synthetic method of penoxsulam. The improved synthetic method comprises the following steps: taking a strong-alkalinity substance, difluoroethanol and 2-fluoro-6-trifluoromethyl-N-(5,8-dimethoxy[1,2,4]triazolo[1,5-c]pyridine-2-yl)benzsulfamide (hereinafter to be referred as tetrafluorosulfamide) as raw materials; taking the strong-alkalinity substance and the difluoroethanol to react to prepare a solution A (in the presence of the difluoroethanol) which has relatively weak alkalinity and contains F2CH1CH2O-; adding the tetrafluorosulfamide to prepare the penoxsulam. Therefore, all the raw materials are added in sequence and the temperature of a reaction system is controlled; side reaction can be effectively reduced; the content of impurities is reduced, the purity of a product is improved or a purification step is reduced.