Carfentrazone-ethyl was synthesized by one-pot reaction with 1-(5-amino-4-chloro-2- fluorophenyl)-4-(difluoromethyl)-3-methyl-1H-1,2,4-triazol-5(4H)-one(TZLO-A) as raw materials, copper(Ⅰ) chloride(CuCl) as catalyst and t-butyl nitrite(t-BuONO) as diazotized reagent through diazotization and Meerwin arylation reaction in acetonitrile or butanone. The structure of the product was characterized by 1HNMR、13CNMR and MS spectrum. The optimum reaction conditions of synthesis were obtained as follows: the molar ratio of TZLO-A, copper(Ⅰ) chloride, ethyl acrylate, to t-butyl nitrite was 1:(0.6-0.7):13.7:1.5, the adding time of hydrochloric acid and t-butyl nitrite was 20 min and 150 min respectively. Under these conditions, the target product was obtained with a yield of 92.9% and with a purity of 92%.