[目的]依据GB 5009.92—2016《食品安全国家标准 食品中钙的测定》标准中第一法,用火焰原子吸收光谱法测定牛乳中钙含量,评定其不确定度。[方法]建立数学模型,分析该测定过程的不确定度来源,并量化评定,计算合成相对标准不确定度和扩展不确定度。[结果]取置信概率P为95%时,钙含量的扩展不确定度为3.22 mg/100 g,即该乳中钙含量测定结果为X=（123.80±3.22）mg/100g。[结论]不确定度的主要来源是标准工作曲线溶液的配制和标准工作曲线的拟合、测定重复性两个方面,评定不确定度的结果可以为火焰原子吸收光谱法测定牛乳中钙含量的准确性提供参考。

[Objective] According to the first method in GB 5009.92-2016 Determination of Calcium in Food under National Food Safety Standard,the content of calcium in milk was determined by flame atomic absorption spectrometry and its uncertainty was evaluated. [Method] A mathematical model was established to analyze the source of uncertainty in the measurement process, quantify the evaluation, and calculate the synthetic relative standard uncertainty and extended uncertainty. [Result] When the confidence probability P is 95%, the extended uncertainty of calcium content is 3.22 mg/100g, that is, the determination result of calcium content in the milk is X=（123.80±3.22）mg/100g. [Conclusion]The main sources of uncertainty are the preparation of the standard working curve solution, the fitting of the standard working curve and the determination repeatability. The evaluation results of uncertainty can provide a reference for the accuracy of determination of calcium content in milk by flame atomic absorption spectrometry.