Abstract: By improving the literature methods, the original drug of the 4-hydroxyphenylpyruvate dioxygenase(HPPD) herbicide fenquinotrione was successfully prepared, and it was found to contain 4 major impurities with a mass fraction of more than 1‰. The impurities were successfully synthesized by the designed routes, and none of them were reported in the literature. The structures of the impurities were confirmed by the high-performance liquid chromatography (HPLC), high-resolution mass spectrometry(HRMS) and nuclear magnetic resonance hydrogen (¹H NMR)/carbon spectrometry (¹³C NMR). Finally, the formation mechanism of the impurities were analyzed by discussing the synthetic route, and some optimization measures were proposed. This study has certain reference value for the subsequent process optimization and quality control during the production of fenquinotrione.