Abstract: According to evaluation and expression of Uncertainly in Measurement (JJF1059-1999) .A mathematical model was established to assess the uncertainty for determining the concentration of Sulfur Dioxide Residue in Peeled Shredded Squid by no mercury salt colorimetry.Various sources of uncertainty were assessed.The influence of the identified uncertainty of the analytical result was evaluated.The results showed that the key factors of uncertainty were Sulfur dioxide standard substance and the fitting of calibration curve thirdly.Sample weighting, voluming and repeated experiment were subordinate factors of uncertainty.The concentration of lead was 13.35mg /kg and the expanded uncertainty was 0.52mg /kg (95%, k = 2) .It can be used as a reference for the laboratory in the detection process to further improve the reliability of the test data and consistency.