[Objective] To establish an uncertainty evaluation model for determining the total mercury content in dairy products by atomic fluorescence spectrometry,identify the key sources of error,and provide a scientific basis for laboratory quality control and optimization of detection standards.[Method] According to the first method of the first chapter of “GB 5009.17—2021 Food Safety National Standard - Determination of Total Mercury and Organic Mercury in Food”,the total mercury content in the milk samples spiked with mercury was determined. By systematically analyzing each uncertainty component in the measurement process,the contribution of each component to the combined uncertainty was quantified,and the expanded uncertainty was calculated.[Result] The total mercury content in the spiked milk sample was（0.009 7±0.001 3）mg/kg（k=2）. The recovery rate,repeatability measurement,and blank solution were the main sources of uncertainty,while secondary sources included standard curve fitting,standard solution,sample liquid dilution and sample weighing. Subsequently,by optimizing pre-treatment methods （such as improving the digestion process）,increasing the number of parallel determinations,and strictly controlling the test blanks,the synthetic uncertainty can be significantly reduced.[Conclusion] Atomic fluorescence spectrometry is suitable for the highly sensitive detection of total mercury in dairy products. The uncertainty in the evaluation process was mainly dominated by recovery rate,repeatability measurement,and blank solution. By standardizing the operation process and specifically optimizing these aspects,the accuracy and reliability of the detection results can be improved,providing technical support for the safety supervision of dairy products.