Abstract:The uncertainty of measurement in the determination of aflatoxin B1 in maize by ultra performance liquid chromatography （UPLC）was evaluated.According to the national metrology technical specifications described in CNAS-GL006-2018 ＜Guidance on Evaluating the Uncertainty in Chemical Analysis＞ and JJF 1059.1-1999 ＜Evaluation and Expression of Uncertainty in Measurement ＞ ，a mathematical model was established to evaluate the uncertainty for determining aflatoxin B1 in maize.The sources of uncertainty that may be introduced were analyzed and each component of uncertainty was quantified and used to calculate combined uncertainty.The results showed that an expended uncertainty of 3.60 μg/kg （k=2）was obtained for the determination of 0.14 μg/kg of aflatoxin B1 in maize，and the sample heterogeneity was the main sources of uncertainty.The other factors were the recover ratio，the preparation of standard solution and the sample solution volume，and the corresponding relative standard uncertainties were 0.014 0，0.009，0.007，0.005 8.