An ultra performance liquid chromatography-quadrupole time-of-flight mass spectrometric(UPLC-Q-TOF-MS) method with purification of aflatoxin immunoaffinity column was established for the determination of aflatoxin B1(AFB1) in fermented dark tea.The sample was extracted with methanol-water(7∶3,by volume),and separated with an HSS T3 column(100 mm×2.1 mm,1.8 μm),then scanned in positive ion scanning mode and analyzed in Full ms-dd-MS/MS mode.The results showed that there existed good linearities for aflatoxin B1 in 33 kinds of fermented dark tea in corresponding concentration range,with their correlation coefficients all greater than 0.999.The recoveries were in the range of 86.4%-98.0%with the relative standard deviations(RSDs) of 0.3%-1.7%.The limits of detection(LODs,S/N≥3) and the limits of quantification(LOQs,S/N≥10) were 0.06 μg/kg and 019 μg/kg,respectively.This method was used to detect AFB1 in 33 tea samples collected from the local markets,and negative results were obtained.The results showed that the contents of AFB1 were within a reasonable range.This method was accurate,rapid and simple,and was suitable for the daily detection of AFB1.