Abstract: Objective To establish ion chromatography (IC) as uncertainty assessment method for determining the concentration of Nitrate and Nitrite in foods and provide the basis for simplification of assessment method and evaluation of detecting results. Methods The calculation formula of the uncertainty was deduced, and factors of uncertainty was analyzed and calculated with uncertainty theory. Results The relative expanded uncertainty of NO₂^- and NO₃^- was 3.815%和3.055%, of which the uncertainty from the pre-treatment were 3.432% and 2.757%, from the concentration of sample solution gained from standard solution and standard curve were 1.665% and 1.313%, and from set volume and weighing sample were 0.076% and 0.029%. Conclusion the pre-treatment and the concentration of sample solution were the main sources of uncertainty, and in the future, the uncertainty of similar method could be focused on evaluating the sample pre-treatment and solution concentration.