Abstract:Uncertainty for determination of sodium in milk powder by inductively coupled plasma atomic emis－ sion spectrum （ICP-AES） was evaluated. A mathematic model was established by analyzing the uncertainty sources from different parts. The uncertainty of sodium content was calculated by synthesis and extension of each uncertainty components. The results showed that recovery rate， fitted linear equation for the standard curve and measurement repeatability were the main sources of uncertainties. The sodium content in milk powder was deter－ mined to be（465±40）mg/100 g（k=2）.