A method was developed for the determination of benzoquanmine in liquid products of milk by high performance liquid chromatography-tandem mass spectrometry(HPLC-MS/MS).The conditions of extraction and parameters of LC-MS were optimized.The sample was enriched and purified with an LC-C18 SPE cartridge，then separated on a ZORBAX Eclipse Plus C18 column using a mixture of acetonitrile-water(15∶85) as mobile phase at a flow rate of 0.3 mL/min.The detection of benzoquanmine was performed by mass spectrometry(ESI-MS) under positive-ion electrospray ionization mode.The two precursor-product ion pairs，m/z 104.1 and m/z 146.0，were used as the quantitative and qualificative ions，respectively.The external standard method was used for quantitative analysis.The results showed that a good linearity for benzoquanmine existed in the range of 2-100 μg/L with a correlation coefficient of 0.999 1.The limits of detection(LODs) and limits of quantitation(LOQs) were 1.0 μg/kg and 3.0 μg/kg，respectively.The average recoveries of benzoquanmine at three spiked levels were in the range of 77%-105%，with relative standard deviations(RSDs) of 2.3%-5.0%.The proposed method was simple and accurate,and was suitable for the determination of benzoquanmine in liquid products of milk.