OBJECTIVE： To isolate， purify and identify the impurities in the synthesis products of 4′ ，7-diethyl tectorigenin， and to provide reference for its quality control. METHODS： LC-MS/MS was adopted to analyze the impurities in the synthesis products of 4′ ，7-diethyl tectorigenin； the potential structure of each impurity was deduced according to mass-charge ratio [M+H]+ of ion peak. The major impurities were isolated by silica gel column chromatography using chloroform-methanol （gradient elution， 20 ∶ 1， 10 ∶ 1， 8 ∶ 1， 6 ∶ 1， 5 ∶ 1， 3 ∶ 1， 2 ∶ 1， 1 ∶ 1， 0 ∶ 1， V/V）. The structures of the impurities were identified by UV spectroscopy， IR spectroscopy and NMR. RESULTS： Totally 21 impurities were detected in the synthesis products of 4′ ，7-diethyl tectorigenin. The potential structures of 17 impurities were elucidated； 4 impurity monomers were isolated and purified. The impurities were identified as 2-hydroxy-3-methoxy-4，6，4′ -triethoxy deoxybenzoin （1）， 2，6-dihydroxy-3-methoxy-4，4′ -diethoxy deoxybenzoin （2）， tectorigenin （3） and tectoridin （4）. impurity 2 was reported for the first time. CONCLUSIONS： The result can provide important evidence for the optimization of synthesis process and quality control of 4′ ，7-diethyl tectorigenin.